Electron transport layer comprising a matrix compound mixture for an organic light-emitting diode (OLED)

ABSTRACT

The present invention is directed to an organic light emitting diode ( 100 ) comprising:
         at least one anode electrode ( 120 );   at least one emission layer ( 150 ), wherein the emission layer comprises at least one emitter dopant that emits visible light at operation of the OLED ( 100 );   an electron transport layer stack ( 160 ) of at least two electron transport layers ( 161/162 ), and wherein       a) the first electron transport layer ( 161 ) comprises i) a first organic aromatic matrix compound having a MW of about ≥400 to about ≤1000 and a dipole moment of about ≥0 Debye and about ≤2.5 Debye, wherein the first electron transport layer ( 161 ) is free of a polar organic aromatic phosphine compound; and   b) the second electron transport layer ( 162 ) comprises two organic aromatic matrix compounds, which are a mixture of:
       i) the first organic aromatic matrix compound; and   ii) a polar organic aromatic phosphine compound having a MW of about ≥400 to about ≤1000, and a dipole moment of about &gt;2.5 Debye and about ≤10 Debye; and   at least one cathode electrode layer ( 190 ); wherein
 
the electron transport layer stack ( 160 ) is arranged between the emission layer ( 150 ) and the cathode electrode layer ( 190 ), the first electron transport layer ( 161 ) is in direct contact with the second electron transport layer ( 162 ), and wherein the first electron transport layer ( 161 ) is arranged nearer to the emission layer ( 150 ) and the second electron transport layer ( 162 ) is arranged nearer to the cathode electrode layer ( 190 ).

CROSS REFERENCE TO RELATED APPLICATION

This application is a U.S. national stage application ofPCT/EP2017/053501, filed Feb. 16, 2017, which claims priority toEuropean Application No. 16156578.3, filed Feb. 19, 2016. The contentsof these applications are hereby incorporated by reference.

DESCRIPTION

The present invention relates to an organic light-emitting diode (OLED)comprising an electron transport layer stack having an electrontransport layer containing a matrix compound mixture, and a method ofmanufacturing the organic light-emitting diode (OLED) comprising theelectron transport layer stack.

DESCRIPTION OF THE RELATED ART

Organic light-emitting diodes (OLEDs), which are self-emitting devices,have a wide viewing angle, excellent contrast, quick response, highbrightness, excellent driving voltage characteristics, and colorreproduction. A typical OLED includes an anode electrode a holeinjection layer (HIL), a hole transport layer (HTL), an emission layer(EML), an electron transport layer (ETL), and a cathode electrode, whichare sequentially stacked on a substrate. In this regard, the HIL, theHTL, the EML, and the ETL are thin films formed from organic compounds.

When a voltage is applied to the anode electrode and the cathodeelectrode, holes injected from the anode electrode move to the EML, viathe HIL and HTL, and electrons injected from the cathode electrode moveto the EML, via the ETL. The holes and electrons recombine in the EML togenerate excitons.

WO 2016/001283 A1 refers to an organic light-emitting diode (OLED)comprising an emission layer and an electron transport layer stack of atleast two electron transport layers, wherein a first electron transportlayer and a second electron transport layer comprises at least onematrix compound and in addition, the first electron transport layercomprises a first lithium halide or a first lithium organic complex; andthe second electron transport layer comprises a second lithium halide ora second lithium organic complex, wherein the first lithium organiccomplex is not the same as the second lithium organic complex, andwherein the first lithium halide is not the same as the second lithiumhalide.

KR 2015 0115688 A refers to an organic light-emitting diode (OLED)comprising a first electron transport layer provided between the cathodeand the light-emitting layer; and a second electron transport layerprovided between the cathode and the first electron transport layer,wherein the second electron transport layer comprises a host material,and one or more n-type dopants selected from alkali metals and alkalineearth metals.

It is still desired to improve the external quantum efficiency (EQE), toreduce operating voltage, improving lifetime of the OLED and/or toincrease the takt time of the OLED manufacturing process.

SUMMARY

One aspect of the present invention is to provide OLEDs with improvedexternal quantum efficiency (EQE) and/or lower operating voltage and/orimproved lifetime and/or increased takt time, for top and/or bottomemission organic light-emitting diodes (OLED).

The invention relates to an organic light emitting diode comprising:

-   -   at least one anode electrode;    -   at least one emission layer, wherein the emission layer        comprises at least one emitter dopant that emits visible light        at operation of the OLED;    -   an electron transport layer stack of at least two electron        transport layers, and wherein    -   a) the first electron transport layer comprises i) a first        organic aromatic matrix compound having a MW of about ≥400 to        about ≤1000 and a dipole moment of about ≥0 Debye and about ≤2.5        Debye, wherein the first electron transport layer is free of a        polar organic aromatic phosphine compound; and    -   b) the second electron transport layer comprises two organic        aromatic matrix compounds, which are a mixture of:        -   i) the first organic aromatic matrix compound; and        -   ii) a polar organic aromatic phosphine compound having a MW            of about ≥400 to about ≤1000, and a dipole moment of            about >2.5 Debye and about ≤10 Debye, preferably of about ≥3            and ≤5 Debye; and    -   at least one cathode electrode layer; wherein        the electron transport layer stack is arranged between the        emission layer and the cathode electrode layer, the first        electron transport layer is in direct contact with the second        electron transport layer, and wherein the first electron        transport layer is arranged nearer to the emission layer and the        second electron transport layer is arranged nearer to the        cathode electrode layer.

The invention relates further to an organic light-emitting diode (OLED)comprising a substrate, an anode electrode, a hole injection layer, ahole transport layer, optional an electron blocking layer, an emissionlayer, optional a hole blocking layer, an electron transport layer stackcomprising a first electron transport layer and a second electrontransport layer, optional an electron injection layer, and a cathodeelectrode layer, wherein the layers are arranged in that order.

The invention relates further to a method of manufacturing the OLED.

DEFINITIONS

The term “OLED”, “organic light emitting diode” and “organiclight-emitting diode” are simultaneously used and have the same meaning.

The term “electron transport layer stack”, also named ETL-stack, meansat least two electron transport layers (ETL) which arranged in directcontact, for example of first and second electrode layer arranged indirect contact. The “electron transport layer stack” may comprise atleast two electron transport layers, at least three electron transportlayers or at least four electron transport layers.

The term “the first organic aromatic matrix compound” is synonymouslyused for “i) a first organic aromatic matrix compound having a MW ofabout ≥400 to about ≤1000 and a dipole moment of about ≥0 Debye andabout ≤2.5 Debye”.

The term “the polar organic aromatic phosphine compound” is synonymouslyused for “ii) a polar organic aromatic phosphine compound having a MW ofabout ≥400 to about ≤1000, and a dipole moment of about >2.5 Debye andabout ≤10 Debye”.

As used herein, “emitter dopant” means a compound which emits visiblelight at operation of the OLED. In the context of the present invention“visible light” means light with a wavelength of about ≥380 nm to about≤780 nm.

In the context of the present specification the term “non-emitterdopant” as used in connection with an electron transport layer (ETL) orelectron transport layer stack means a dopant, which does not contributeto the emission spectrum of the device at operation of the OLED. Inother words, the non-emitter dopant is essentially non-emissive in thevisible region of the electromagnetic spectrum, which are wavelengths ofabout ≥380 nm to about ≤780 nm.

In the context of the present specification the term “essentiallynon-emissive” means that the contribution of the non-emitter dopant tothe emission spectrum at operation of the OLED is less than 10%,preferably less than 5% relative to the emission spectrum.

In the context of the present specification the term “at operation ofthe OLED” means that a voltage of 2 to 10 V is applied. The OLED thatcan be used is an OLED according to the invention, for example an OLEDaccording to the invention of Table 7.

As used herein, “weight percent”, “wt.-%”, “percent by weight”, “% byweight”, and variations thereof refer to a composition, component,substance or agent as the weight of that composition, component,substance or agent of the respective electron transport layer divided bythe total weight of the composition thereof and multiplied by 100. It isunderstood that the total weight percent amount of all components,substances or agents of the respective electron transport layer areselected such that it does not exceed 100 wt.-%.

As used herein, “volume percent”, “vol.-%”, “percent by volume”, “% byvolume”, and variations thereof refer to an elemental metal, acomposition, component, substance or agent as the volume of thatelemental metal, component, substance or agent of the respectiveelectron transport layer divided by the total volume of the respectiveelectron transport layer thereof and multiplied by 100. It is understoodthat the total volume percent amount of all elemental metal, components,substances or agents of the respective cathode electrode layer areselected such that it does not exceed 100 vol.-%.

All numeric values are herein assumed to be modified by the term“about”, whether or not explicitly indicated. As used herein, the term“about” refers to variation in the numerical quantity that can occur.Whether or not, modified by the term “about”, the claims includeequivalents to the quantities.

It should be noted that, as used in this specification and the appendedclaims, the singular forms “a”, “an”, and “the” include plural referentsunless the content clearly dictates otherwise.

The term “free of”, “does not contain”, “does not comprise” does notexclude impurities which may be present in the compounds prior todeposition or in the layers after deposition. Impurities have notechnical effect with respect to the object achieved by the presentinvention.

The term “phosphine compound” or “polar organic aromatic phosphinecompound” means and includes compounds selected from the group oforganic phosphine oxide compound, organic thioxophosphine compound ororganic selenoxophosphine compound.

The term “phosphine compound” as used in the specification and claimscomprises compounds according to formula Ia including phosphole andphosphepine.

The term “alkyl” refers to straight-chain, branched or cyclic alkylgroups.

The alkyl groups can be selected from the group comprising methyl, ethyland the isomers of propyl, butyl or pentyl, such as isopropyl, isobutyl,tert-butyl, sec.-butyl, isopentyl and/or cyclo-hexyl.

The term “alkane-di-yl” as used herein refers to a straight-chain,branched or cyclic alkane-di-yl group. The alkane-di-yl group is asaturated group which is bonded to two phosphorus atoms.

The term “alkene-di-yl” as used herein refers to a group comprisingsingle and double carbon-carbon bonds. Preferably, double bonds andsingle bonds alternate to form a five, six or seven membered ring with aphosphorus atom.

The term “aryl” refers to aromatic groups. The term “aryl” as usedherewith shall encompass phenyl (C6-aryl), fused aromatics, such asnaphthalene, anthracene, phenanthrene, tetracene etc. Furtherencompassed are bi-phenyl and oligo- or polyphenyls, such as terphenyletc. Further encompassed shall be any further aromatic hydrocarbonsubstituents, such as fluorenyl etc.

The term “arylene” refers to aromatic groups. The term “arylene” as usedherewith shall encompass phenylene (C6-arylene), fused aromatics, suchas naphthalene-di-yl, anthracene-di-yl, phenanthrene-di-yl,tetracene-di-yl, binaphthylene-di-yl etc. Further encompassed arebi-phenylene and oligo- or polyphenylenes, such as terphenylene etc.Further encompassed shall be any further aromatic groups, such asfluorene-di-yl etc.

The term “heteroarylene” refers to aromatic heterocycles. The term“heteroarylene” as used herewith shall encompass pyridine-di-yl,quinolone-di-yl, carbazol-di-yl, xanthene-di-yl, phenoxazine-di-yl etc.

Herein, when a first element is referred to as being formed or disposed“on” a second element, the first element can be disposed directly on thesecond element or one or more other elements may be disposed therebetween. When a first element is referred to as being formed or disposed“directly on” a second element, no other elements are disposed therebetween.

The term “contacting sandwiched” refers to an arrangement of threelayers whereby the layer in the middle is in direct contact with the twoadjacent layers.

The anode electrode may be described as anode electrode or anodeelectrode layer.

The cathode electrode may be described as cathode electrode or cathodeelectrode layer.

The composition and/or components of the electron injection layersdiffer from the electron transport layer stack.

The electron transport layer stack is not a cathode electrode, as theydiffer in their composition.

The cathode electrode of the OLED according to the invention may notcomprise a polar organic aromatic phosphine compound or organic aromaticmatrix compound.

The cathode electrode of the OLED according to the invention may notcomprise or consist of an organic compound.

In a preferred embodiment, the cathode electrode layer may be free oforganic compounds, organic metal complexes and metal halides.

The electron transport layer stack, the electron injection layer/s andcathode electrode layer/s may differ each in their composition.

The electron injection layer/s and cathode electrode layer/s may differeach in their composition.

The operating voltage, also named U, is measured in Volt (V) at 10milliAmpere per square centimetre (mA/cm²) in bottom emission devicesand at 15 mA/cm² in top emission devices.

The external quantum efficiency, also named EQE, is measured in percent(%).

The color space is described by coordinates CIE-x and CIE-y(International Commission on Illumination 1931). For blue emission theCIE-y is of particular importance. A smaller CIE-y denotes a deeper bluecolor.

The highest occupied molecular orbital, also named HOMO, and lowestunoccupied molecular orbital, also named LUMO, are measured in electronvolt (eV). The HOMO and LUMO are measured with cyclic voltammetry insolution.

The dipole moment is determined through quantum-chemical calculationsand measured in Debye (D).

The triplet level T₁ is determined through quantum-chemical calculationsand measured in electron volt (eV).

The term “MW” means molar mass and is measured in gramm per mol (g/mol).

If not other way stated the Relative humidity (abbreviated RH) is 40%and the temperature is 23° C.

OTHER EMBODIMENTS

According to an aspect of the present invention, there is provided anorganic light emitting diode (OLED) comprising:

-   -   at least one anode electrode;    -   at least one emission layer, wherein the emission layer        comprises at least one emitter dopant that emits visible light        at operation of the OLED;    -   an electron transport layer stack of at least two electron        transport layers, and wherein    -   a) the first electron transport layer comprises i) a first        organic aromatic matrix compound having a MW of about ≥400 to        about ≤1000 and a dipole moment of about ≥0 Debye and about ≤2.5        Debye, wherein the first electron transport layer is free of a        polar organic aromatic phosphine compound; and    -   b) the second electron transport layer comprises two organic        aromatic matrix compounds, which are a mixture of:        -   i) the first organic aromatic matrix compound; and        -   ii) a polar organic aromatic phosphine compound having a MW            of about ≥400 to about ≤1000, and a dipole moment of            about >2.5 Debye and about ≤10 Debye; and    -   at least one cathode electrode layer; wherein    -   the electron transport layer stack is arranged between the        emission layer and the cathode electrode layer, the first        electron transport layer is in direct contact with the second        electron transport layer, and wherein the first electron        transport layer is arranged nearer to the emission layer and the        second electron transport layer is arranged nearer to the        cathode electrode layer; and wherein the second electron        transport layer comprises:    -   ≥50 wt.-% to ≤95 wt.-%, preferably ≥60 wt.-% to ≤90 wt.-%, and        more preferred 70 wt.-% to ≤90 wt.-%, and most preferred about        80 wt.-%. of i) the first organic aromatic matrix compound; and    -   ≥5 wt.-% to ≤50 wt.-%, preferably ≥10 wt.-% to ≤40 wt.-%, and        more preferred ≥10 wt.-% to ≤30 wt.-%, and most preferred about        20 wt.-%, of ii) the polar organic aromatic phosphine compound;        wherein the wt.-% is based on the total weight of i) and ii) of        the second electron transport layer.

According to another aspect of the present invention, there is providedan organic light emitting diode (OLED) comprising:

-   -   at least one anode electrode;    -   at least one emission layer, wherein the emission layer        comprises at least one emitter dopant that emits visible light        at operation of the OLED;    -   an electron transport layer stack of at least two electron        transport layers, and wherein    -   a) the first electron transport layer comprises i) a first        organic aromatic matrix compound having a MW of about ≥400 to        about ≤1000 and a dipole moment of about ≥0 Debye and about ≤2.5        Debye, wherein the first electron transport layer is free of a        polar organic aromatic phosphine compound; and    -   b) the second electron transport layer comprises two organic        aromatic matrix compounds, which are a mixture of:        -   i) the first organic aromatic matrix compound; and        -   ii) a polar organic aromatic phosphine compound having a MW            of about ≥400 to about ≤1000, and a dipole moment of            about >2.5 Debye and about ≤10 Debye; and    -   at least one cathode electrode layer; wherein

the electron transport layer stack is arranged between the emissionlayer and the cathode electrode layer, the first electron transportlayer is in direct contact with the second electron transport layer, andwherein the first electron transport layer is arranged nearer to theemission layer and the second electron transport layer is arrangednearer to the cathode electrode layer; and wherein the second electrontransport layer comprises at least one non-emitter dopant and comprises:

-   -   ≥30 wt.-% to ≤95 wt.-%, preferably ≥60 wt.-% to ≤90 wt.-%, and        more preferred ≥70 wt.-% to ≤90 wt.-%, and most preferred about        80 wt.-%. of i) the first organic aromatic matrix compound; and    -   ≥5 wt.-% to ≤50 wt.-%, preferably ≥10 wt.-% to ≤40 wt.-%, and        more preferred ≥10 wt.-% to ≤30 wt.-%, and most preferred about        20 wt.-%, of ii) the polar organic aromatic phosphine compound;        wherein the wt.-% is based on the total weight of i) and ii) of        the second electron transport layer.

According to another aspect of the present invention, there is providedan organic light emitting diode (OLED) comprising:

-   -   at least one anode electrode;    -   at least one emission layer, wherein the emission layer        comprises at least one emitter dopant that emits visible light        at operation of the OLED;    -   an electron transport layer stack of at least two electron        transport layers, and wherein    -   a) the first electron transport layer comprises i) a first        organic aromatic matrix compound having a MW of about ≥400 to        about ≤1000 and a dipole moment of about ≥0 Debye and about ≤2.5        Debye, wherein the first electron transport layer is free of a        polar organic aromatic phosphine compound; and    -   b) the second electron transport layer comprises two organic        aromatic matrix compounds, which are a mixture of:        -   i) the first organic aromatic matrix compound; and        -   ii) a polar organic aromatic phosphine compound having a MW            of about ≥400 to about ≤1000, and a dipole moment of            about >2.5 Debye and about ≤10 Debye; and    -   at least one cathode electrode layer; wherein        the electron transport layer stack is arranged between the        emission layer and the cathode electrode layer, the first        electron transport layer is in direct contact with the second        electron transport layer, and wherein the first electron        transport layer is arranged nearer to the emission layer and the        second electron transport layer is arranged nearer to the        cathode electrode layer; and wherein the second electron        transport layer comprises at least one non-emitter dopant,        wherein the non-emitter dopant is a metal compound, preferably        the metal compound is selected from the group comprising a metal        halide, a metal organic complex and/or a zero-valent metal; and        more preferred the metal organic complex has the formula VII:

-   -   wherein M is an alkali metal ion, each of A¹-A⁴ is independently        selected from substituted or unsubstituted C₆-C₂₀ aryl or        substituted or unsubstituted C₂-C₂₀ heteroaryl, even more        preferred M is lithium ion, and most preferred lithium        tetra(1H-pyrazol-1-yl)borate; and the second electron transport        layer comprises:    -   ≥50 wt.-% to ≤95 wt.-%, preferably ≥60 wt.-% to ≤90 wt.-%, and        more preferred ≥70 wt.-% to ≤90 wt.-%, and most preferred about        80 wt.-%. of i) the first organic aromatic matrix compound; and    -   ≥5 wt.-% to ≤50 wt.-%, preferably ≥10 wt.-% to ≤40 wt.-%, and        more preferred ≥10 wt.-% to ≤30 wt.-%, and most preferred about        20 wt.-%, of ii) the polar organic aromatic phosphine compound;        wherein the wt.-% is based on the total weight of i) and ii) of        the second electron transport layer.

According to another aspect of the present invention the first electrontransport layer can be free of a non-emitter dopant.

According to another aspect of the present invention the second electrontransport layer may comprises in addition a non-emitter dopant.

According to another aspect of the present invention the non-emitterdopant is a metal compound, preferably the metal compound is selectedfrom the group comprising a metal halide, a metal organic complex and/ora zero-valent metal.

According to another aspect of the present invention the non-emitterdopant is selected from the group comprising a metal halide, a metalorganic complex and/or a zero-valent metal.

According to another aspect of the present invention the non-emitterdopant is a zero-valent metal.

According to another aspect of the present invention the second electrontransport layer may comprises in addition a non-emitter dopant that is azero-valent metal.

According to another aspect of the present invention, there is providedan organic light emitting diode (OLED) comprising:

-   -   at least one anode electrode;    -   at least one emission layer, wherein the emission layer        comprises at least one emitter dopant that emits visible light        at operation of the OLED;    -   an electron transport layer stack of at least two electron        transport layers, and wherein    -   a) the first electron transport layer comprises i) a first        organic aromatic matrix compound having a MW of about ≥400 to        about ≤1000 and a dipole moment of about ≥0 Debye and about ≤2.5        Debye, wherein the first electron transport layer is free of a        polar organic aromatic phosphine compound; and    -   b) the second electron transport layer comprises two organic        aromatic matrix compounds, which are a mixture of:        -   i) the first organic aromatic matrix compound; and        -   ii) a polar organic aromatic phosphine compound having a MW            of about ≥400 to about ≤1000, and a dipole moment of            about >2.5 Debye and about ≤10 Debye; and    -   at least one cathode electrode layer; wherein

the electron transport layer stack is arranged between the emissionlayer and the cathode electrode layer, the first electron transportlayer is in direct contact with the second electron transport layer, andwherein the first electron transport layer is arranged nearer to theemission layer and the second electron transport layer is arrangednearer to the cathode electrode layer; and wherein the first electrontransport layer comprises ≥90 wt.-% to ≤100 wt.-%, preferably ≥95 wt.-%to ≤98 wt.-%, of the first organic aromatic matrix compound.

According to another aspect of the present invention, there is providedan organic light emitting diode (OLED) comprising:

-   -   at least one anode electrode;    -   at least one emission layer, wherein the emission layer        comprises at least one emitter dopant that emits visible light        at operation of the OLED;    -   an electron transport layer stack of at least two electron        transport layers, and wherein    -   a) the first electron transport layer comprises i) a first        organic aromatic matrix compound having a MW of about ≥400 to        about ≤1000 and a dipole moment of about ≥0 Debye and about ≤2.5        Debye, wherein the first electron transport layer is free of a        polar organic aromatic phosphine compound; and    -   b) the second electron transport layer comprises two organic        aromatic matrix compounds, which are a mixture of:        -   i) the first organic aromatic matrix compound; and        -   ii) a polar organic aromatic phosphine compound having a MW            of about ≥400 to about ≤1000, and a dipole moment of            about >2.5 Debye and about ≤10 Debye; and    -   at least one cathode electrode layer; wherein

the electron transport layer stack is arranged between the emissionlayer and the cathode electrode layer, the first electron transportlayer is in direct contact with the second electron transport layer, andwherein the first electron transport layer is arranged nearer to theemission layer and the second electron transport layer is arrangednearer to the cathode electrode layer; and wherein the first electrontransport layer comprises a non-emitter dopant and comprises ≥90 wt.-%to ≤100 wt.-%, preferably ≥95 wt.-% to ≤98 wt.-%, of the first organicaromatic matrix compound.

According to another aspect of the present invention, there is providedan organic light emitting diode (OLED) comprising:

-   -   at least one anode electrode;    -   at least one emission layer, wherein the emission layer        comprises at least one emitter dopant that emits visible light        at operation of the OLED;    -   an electron transport layer stack of at least two electron        transport layers, and wherein    -   a) the first electron transport layer comprises i) a first        organic aromatic matrix compound having a MW of about ≥400 to        about ≤1000 and a dipole moment of about ≥0 Debye and about ≤2.5        Debye, wherein the first electron transport layer is free of a        polar organic aromatic phosphine compound; and    -   b) the second electron transport layer comprises two organic        aromatic matrix compounds, which are a mixture of:        -   i) the first organic aromatic matrix compound; and        -   ii) a polar organic aromatic phosphine compound having a MW            of about ≥400 to about ≤1000, and a dipole moment of            about >2.5 Debye and about ≤10 Debye; and    -   at least one cathode electrode layer; wherein

the electron transport layer stack is arranged between the emissionlayer and the cathode electrode layer, the first electron transportlayer is in direct contact with the second electron transport layer, andwherein the first electron transport layer is arranged nearer to theemission layer and the second electron transport layer is arrangednearer to the cathode electrode layer; and wherein the first electrontransport layer comprises ≥90 wt.-% to ≤100 wt.-%, preferably ≥95 wt.-%to ≤98 wt.-%, of the first organic aromatic matrix compound; and thesecond electron transport layer comprises:

-   -   ≥50 wt.-% to ≤95 wt.-%, preferably ≥60 wt.-% to ≤90 wt.-%, and        more preferred ≥70 wt.-% to ≤90 wt.-%, and most preferred about        80 wt.-%. of i) the first organic aromatic matrix compound; and    -   ≥5 wt.-% to ≤50 wt.-%, preferably ≥10 wt.-% to ≤40 wt.-%, and        more preferred ≥10 wt.-% to ≤30 wt.-%, and most preferred about        20 wt.-%, of ii) the polar organic aromatic phosphine compound;        wherein the wt.-% is based on the total weight of i) and ii) of        the second electron transport layer.

According to another aspect of the present invention, there is providedan organic light emitting diode (OLED) comprising:

-   -   at least one anode electrode;    -   at least one emission layer, wherein the emission layer        comprises at least one emitter dopant that emits visible light        at operation of the OLED;    -   an electron transport layer stack of at least two electron        transport layers, and wherein    -   a) the first electron transport layer comprises i) a first        organic aromatic matrix compound having a MW of about ≥400 to        about ≤1000 and a dipole moment of about ≥0 Debye and about ≤2.5        Debye, wherein the first electron transport layer is free of a        polar organic aromatic phosphine compound; and    -   b) the second electron transport layer comprises two organic        aromatic matrix compounds, which are a mixture of:        -   i) the first organic aromatic matrix compound; and        -   ii) a polar organic aromatic phosphine compound having a MW            of about ≥400 to about ≤1000, and a dipole moment of            about >2.5 Debye and about ≤10 Debye; and    -   at least one cathode electrode layer; wherein        the electron transport layer stack is arranged between the        emission layer and the cathode electrode layer, the first        electron transport layer is in direct contact with the second        electron transport layer, and wherein the first electron        transport layer is arranged nearer to the emission layer and the        second electron transport layer is arranged nearer to the        cathode electrode layer; and wherein the first electron        transport layer comprises a non-emitter dopant and comprises ≥90        wt.-% to ≤100 wt.-%, preferably ≥95 wt.-% to ≤98 wt.-%, of the        first organic aromatic matrix compound; and the second electron        transport layer comprises a non-emitter dopant and comprises:    -   ≥50 wt.-% to ≤95 wt.-%, preferably ≥60 wt.-% to ≤90 wt.-%, and        more preferred ≥70 wt.-% to ≤90 wt.-%, and most preferred about        80 wt.-%. of i) the first organic aromatic matrix compound; and    -   ≥5 wt.-% to ≤50 wt.-%, preferably ≥10 wt.-% to ≤40 wt.-%, and        more preferred ≥10 wt.-% to 30 wt.-%, and most preferred about        20 wt.-%, of ii) the polar organic aromatic phosphine compound;        wherein the wt.-% is based on the total weight of i) and ii) of        the second electron transport layer.

According to an aspect of the present invention, there is provided anorganic light emitting diode (OLED) comprising:

-   -   at least one anode electrode;    -   at least one emission layer, wherein the emission layer        comprises at least one emitter dopant that emits visible light        at operation of the OLED;    -   an electron transport layer stack of at least two electron        transport layers, and wherein    -   a) the first electron transport layer consist of i) a first        organic aromatic matrix compound having a MW of about ≥400 to        about ≤1000 and a dipole moment of about ≥0 Debye and about ≤2.5        Debye, wherein the first electron transport layer is free of a        polar organic aromatic phosphine compound; and    -   b) the second electron transport layer comprises two organic        aromatic matrix compounds, which are a mixture of:        -   i) the first organic aromatic matrix compound; and        -   ii) a polar organic aromatic phosphine compound having a MW            of about ≥400 to about ≤1000, and a dipole moment of            about >2.5 Debye and about ≤10 Debye; and    -   at least one cathode electrode layer; wherein        the electron transport layer stack is arranged between the        emission layer and the cathode electrode layer, the first        electron transport layer is in direct contact with the second        electron transport layer, and wherein the first electron        transport layer is arranged nearer to the emission layer and the        second electron transport layer is arranged nearer to the        cathode electrode layer.

According to another aspect of the present invention, there is providedan organic light emitting diode (OLED) comprising:

-   -   at least one anode electrode;    -   at least one emission layer, wherein the emission layer        comprises at least one emitter dopant that emits visible light        at operation of the OLED;    -   an electron transport layer stack of at least two electron        transport layers, wherein the electron transport layer stack is        free of an emitter dopant which emits visible light at operation        of the OLED, and wherein    -   a) the first electron transport layer comprises i) a first        organic aromatic matrix compound having a MW of about ≥400 to        about ≤1000 and a dipole moment of about ≥0 Debye and about ≤2.5        Debye, wherein the first electron transport layer is free of a        polar organic aromatic phosphine compound; and    -   b) the second electron transport layer comprises two organic        aromatic matrix compounds, which are a mixture of:        -   i) the first organic aromatic matrix compound; and        -   ii) a polar organic aromatic phosphine compound having a MW            of about ≥400 to about ≤1000, and a dipole moment of            about >2.5 Debye and about ≤10 Debye; and    -   at least one cathode electrode layer; wherein        the electron transport layer stack is arranged between the        emission layer and the cathode electrode layer, the first        electron transport layer is in direct contact with the second        electron transport layer, and wherein the first electron        transport layer is arranged nearer to the emission layer and the        second electron transport layer is arranged nearer to the        cathode electrode layer.

According to another aspect of the present invention, there is providedan organic light emitting diode (OLED) comprising:

-   -   at least one anode electrode;    -   at least one emission layer, wherein the emission layer        comprises at least one emitter dopant that emits visible light        at operation of the OLED;    -   an electron transport layer stack of at least two electron        transport layers, wherein the electron transport layer stack is        free of an emitter dopant which emits visible light at operation        of the OLED, and wherein the first electron transport layer is        free of a non-emitter dopant and the second electron transport        layer comprises a non-emitter dopant, and wherein    -   a) the first electron transport layer comprises i) a first        organic aromatic matrix compound having a MW of about ≥400 to        about ≤1000 and a dipole moment of about ≥0 Debye and about ≤2.5        Debye, wherein the first electron transport layer is free of a        polar organic aromatic phosphine compound; and    -   b) the second electron transport layer comprises two organic        aromatic matrix compounds, which are a mixture of:        -   i) the first organic aromatic matrix compound; and        -   ii) a polar organic aromatic phosphine compound having a MW            of about ≥400 to about ≤1000, and a dipole moment of            about >2.5 Debye and about ≤10 Debye; and    -   at least one cathode electrode layer; wherein        the electron transport layer stack is arranged between the        emission layer and the cathode electrode layer, the first        electron transport layer is in direct contact with the second        electron transport layer, and wherein the first electron        transport layer is arranged nearer to the emission layer and the        second electron transport layer is arranged nearer to the        cathode electrode layer.

According to another aspect of the present invention, there is providedan organic light emitting diode (OLED) comprising:

-   -   at least one anode electrode;    -   at least one emission layer, wherein the emission layer        comprises at least one emitter dopant that emits visible light        at operation of the OLED;    -   an electron transport layer stack of at least two electron        transport layers, wherein the electron transport layer stack is        free of an emitter dopant which emits visible light at operation        of the OLED, and wherein    -   a) the first electron transport layer consist of first organic        aromatic matrix compound having a MW of about ≥400 to about        ≤1000 i) a and a dipole moment of about ≥0 Debye and about ≤2.5        Debye, wherein the first electron transport layer is free of a        polar organic aromatic phosphine compound; and    -   b) the second electron transport layer comprises a non-emitter        dopant and two organic aromatic matrix compounds, which are a        mixture of:        -   i) the first organic aromatic matrix compound; and        -   ii) a polar organic aromatic phosphine compound having a MW            of about ≥400 to about ≤1000, and a dipole moment of            about >2.5 Debye and about ≤10 Debye; and    -   at least one cathode electrode layer; wherein        the electron transport layer stack is arranged between the        emission layer and the cathode electrode layer, the first        electron transport layer is in direct contact with the second        electron transport layer, and wherein the first electron        transport layer is arranged nearer to the emission layer and the        second electron transport layer is arranged nearer to the        cathode electrode layer.

According to another aspect of the present invention, there is providedan organic light emitting diode (OLED) comprising:

-   -   at least one anode electrode;    -   at least one emission layer, wherein the emission layer        comprises at least one emitter dopant that emits visible light        at operation of the OLED;    -   an electron transport layer stack of at least two electron        transport layers, wherein the electron transport layer stack is        free of an emitter dopant which emits visible light at operation        of the OLED, and wherein    -   a) the first electron transport layer consist of i) a first        organic aromatic matrix compound having a MW of about ≥400 to        about ≤1000 and a dipole moment of about ≥0 Debye and about ≤2.5        Debye, wherein the first electron transport layer is free of a        polar organic aromatic phosphine compound; and    -   b) the second electron transport layer consist of a non-emitter        dopant and two organic aromatic matrix compounds, which are a        mixture of:        -   i) the first organic aromatic matrix compound; and        -   ii) a polar organic aromatic phosphine compound having a MW            of about ≥400 to about ≤1000, and a dipole moment of            about >2.5 Debye and about ≤10 Debye; and    -   at least one cathode electrode layer; wherein        the electron transport layer stack is arranged between the        emission layer and the cathode electrode layer, the first        electron transport layer is in direct contact with the second        electron transport layer, and wherein the first electron        transport layer is arranged nearer to the emission layer and the        second electron transport layer is arranged nearer to the        cathode electrode layer.

According to another aspect of the present invention, there is providedan organic light emitting diode (OLED) comprising:

-   -   at least one anode electrode;    -   at least one emission layer, wherein the emission layer        comprises at least one emitter dopant that emits visible light        at operation of the OLED;    -   an electron transport layer stack of at least two electron        transport layers, and wherein    -   a) the first electron transport layer comprises i) a first        organic aromatic matrix compound having a MW of about ≥400 to        about ≤1000 and a dipole moment of about ≥0 Debye and about ≤2.5        Debye, wherein the first electron transport layer is free of:        -   a polar organic aromatic phosphine compound, aryl compound            with a triplet level≥2.9 eV, phenyltriazole, benzimidazole,            phenanthroline, oxadiazole, benzooxazole, oxazole,            quinazoline, benzo[h]quinazoline, pyrido[3,2-h]quinazoline,            pyrimido [4,5-f] quinazoline, quinoline, benzoquinoline,            pyrrolo[2,1-a]isoquinolin and benzofuro[2,3-d]pyridazine;    -   b) the second electron transport layer comprises two organic        aromatic matrix compounds, which are a mixture of:        -   i) the first organic aromatic matrix compound; and        -   ii) a polar organic aromatic phosphine compound having a MW            of about ≥400 to about ≤1000, and a dipole moment of            about >2.5 Debye and about ≤10 Debye; and    -   at least one cathode electrode layer; wherein        the electron transport layer stack is arranged between the        emission layer and the cathode electrode layer, the first        electron transport layer is in direct contact with the second        electron transport layer, and wherein the first electron        transport layer is arranged nearer to the emission layer and the        second electron transport layer is arranged nearer to the        cathode electrode layer.

The invention relates further to an organic light-emitting diode (OLED)comprising a substrate, an anode electrode, a hole injection layer, ahole transport layer, optional an electron blocking layer, an emissionlayer, optional a hole blocking layer, an electron transport layer stackcomprising a first electron transport layer and a second electrontransport layer, optional an electron injection layer, and a cathodeelectrode layer, wherein the layers are arranged in that order.

According to another aspect of the present invention, there is providedan organic light emitting diode (OLED) comprising:

-   -   at least one anode electrode;    -   at least one emission layer, wherein the emission layer        comprises at least one emitter dopant that emits visible light        at operation of the OLED;    -   an electron transport layer stack of at least two electron        transport layers, wherein the electron transport layer stack is        free of an emitter dopant which emits visible light at operation        of the OLED, and wherein    -   a) the first electron transport layer comprises i) a first        organic aromatic matrix compound having a MW of about ≥400 to        about ≤1000 and a dipole moment of about ≥0 Debye and about ≤2.5        Debye, wherein the first electron transport layer is free of:        -   a polar organic aromatic, phosphine compound, aryl compound            with a triplet level≥2.9 eV, phenyltriazole, benzimidazole,            phenanthroline, oxadiazole, benzooxazole, oxazole,            quinazoline, benzo[h]quinazoline, pyrido[3,2-h]quinazoline,            pyrimido[4,5-f]quinazoline, quinoline, benzoquinoline,            pyrrolo[2,1-a]isoquinolin and benzofuro[2,3-d]pyridazine;            and    -   b) the second electron transport layer comprises two organic        aromatic matrix compounds, which are a mixture of:        -   i) the first organic aromatic matrix compound; and        -   ii) a polar organic aromatic phosphine compound having a MW            of about ≥400 to about ≤1000, and a dipole moment of            about >2.5 Debye and about ≤10 Debye; and    -   at least one cathode electrode layer; wherein        the electron transport layer stack is arranged between the        emission layer and the cathode electrode layer, the first        electron transport layer is in direct contact with the second        electron transport layer, and wherein the first electron        transport layer is arranged nearer to the emission layer and the        second electron transport layer is arranged nearer to the        cathode electrode layer.

According to another aspect of the present invention, there is providedan organic light emitting diode (OLED) comprising:

-   -   at least one anode electrode;    -   at least one emission layer, wherein the emission layer        comprises at least one emitter dopant that emits visible light        at operation of the OLED;    -   an electron transport layer stack of at least two electron        transport layers, wherein the electron transport layer stack is        free of an emitter dopant which emits visible light at operation        of the OLED, and wherein the first electron transport layer is        free of a non-emitter dopant and the second electron transport        layer (162) comprises a non-emitter dopant, and wherein    -   a) the first electron transport layer comprises i) a first        organic aromatic matrix compound having a MW of about ≥400 to        about ≤1000 and a dipole moment of about ≥0 Debye and about ≤2.5        Debye, wherein the first electron transport layer is free of:        -   a polar organic aromatic phosphine compound, aryl compound            with a triplet level≥2.9 eV, phenyltriazole, benzimidazole,            phenanthroline, oxadiazole, benzooxazole, oxazole,            quinazoline, benzo[h]quinazoline, pyrido[3,2-h]quinazoline,            pyrimido[4,5-f]quinazoline, quinoline, benzoquinoline,            pyrrolo[2,1-a]isoquinolin and benzofuro[2,3-d]pyridazine;            and    -   b) the second electron transport layer comprises two organic        aromatic matrix compounds, which are a mixture of:        -   i) the first organic aromatic matrix compound; and        -   ii) a polar organic aromatic phosphine compound having a MW            of about ≥400 to about ≤1000, and a dipole moment of            about >2.5 Debye and about ≤10 Debye; and    -   at least one cathode electrode layer; wherein        the electron transport layer stack is arranged between the        emission layer and the cathode electrode layer, the first        electron transport layer is in direct contact with the second        electron transport layer, and wherein the first electron        transport layer is arranged nearer to the emission layer and the        second electron transport layer is arranged nearer to the        cathode electrode layer.

According to another aspect of the present invention, there is providedan organic light emitting diode (OLED) comprising:

-   -   at least one anode electrode;    -   at least one emission layer, wherein the emission layer        comprises at least one emitter dopant that emits visible light        at operation of the OLED;    -   an electron transport layer stack of at least two electron        transport layers, wherein the electron transport layer stack is        free of an emitter dopant which emits visible light at operation        of the OLED, and wherein the first electron transport layer is        free of a non-emitter dopant and the second electron transport        layer (162) comprises a non-emitter dopant, and wherein    -   a) the first electron transport layer comprises i) a first        organic aromatic matrix compound having a MW of about ≥400 to        about ≤1000 and a dipole moment of about ≥0 Debye and about ≤2.5        Debye, wherein the first electron transport layer is free of:        -   a polar organic aromatic phosphine compound, aryl compound            compounds with a triplet level≥2.9 eV, phenyltriazole,            benzimidazole, phenanthroline, oxadiazole, benzooxazole,            oxazole, quinazoline, benzo[h]quinazoline, pyrido[3,2-h]            quinazoline, pyrimido[4,5-f]quinazoline, quinoline,            benzoquinoline, pyrrolo[2,1-a] isoquinolin and            benzofuro[2,3-d]pyridazine; and    -   b) the second electron transport layer comprises two organic        aromatic matrix compounds, which are a mixture of:        -   i) the first organic aromatic matrix compound; and        -   ii) a polar organic aromatic phosphine compound having a MW            of about ≥400 to about ≤1000, and a dipole moment of            about >2.5 Debye and about ≤10 Debye; and    -   at least one cathode electrode layer; wherein        the electron transport layer stack is arranged between the        emission layer and the cathode electrode layer, the first        electron transport layer is in direct contact with the second        electron transport layer, and wherein the first electron        transport layer is arranged nearer to the emission layer and the        second electron transport layer is arranged nearer to the        cathode electrode layer; and wherein the second electron        transport layer comprises:    -   ≥50 wt.-% to ≤95 wt.-%, preferably ≥60 wt.-% to ≤90 wt.-%, and        more preferred ≥70 wt.-% to ≤90 wt.-%, and most preferred about        80 wt.-%. of i) the first organic aromatic matrix compound; and    -   ≥5 wt.-% to ≤50 wt.-%, preferably ≥10 wt.-% to ≤40 wt.-%, and        more preferred ≥10 wt.-% to ≤30 wt-%, and most preferred about        20 wt.-%, of ii) the polar organic aromatic phosphine compound;        wherein the wt.-% is based on the total weight of i) and ii) of        the second electron transport layer.

According to another aspect of the present invention, there is providedan organic light emitting diode (OLED) comprising:

-   -   at least one anode electrode;    -   at least one emission layer, wherein the emission layer        comprises at least one emitter dopant that emits visible light        at operation of the OLED;    -   an electron transport layer stack of at least two electron        transport layers, wherein the electron transport layer stack is        free of an emitter dopant which emits visible light at operation        of the OLED, and wherein the first electron transport layer is        free of a non-emitter dopant and the second electron transport        layer (162) comprises a non-emitter dopant, and wherein    -   a) the first electron transport layer comprises i) a first        organic aromatic matrix compound having a MW of about ≥400 to        about ≤1000 and a dipole moment of about ≥0 Debye and about ≤2.5        Debye, wherein the first electron transport layer is free of:    -   a polar organic aromatic phosphine compound, aryl compound        compounds with a triplet level≥2.9 eV, phenyltriazole,        benzimidazole, phenanthroline, oxadiazole, benzooxazole,        oxazole, quinazoline, benzo[h]quinazoline,        pyrido[3,2-h]-quinazoline, pyrimido[4,5-f]quinazoline,        quinoline, benzoquinoline, pyrrolo[2,1-a] isoquinolin and        benzofuro[2,3-d]pyridazine; and    -   b) the second electron transport layer comprises two organic        aromatic matrix compounds, which are a mixture of:        -   i) the first organic aromatic matrix compound; and        -   ii) a polar organic aromatic phosphine compound having a MW            of about ≥400 to about ≤1000, and a dipole moment of            about >2.5 Debye and about ≤10 Debye; and    -   at least one cathode electrode layer; wherein        the electron transport layer stack is arranged between the        emission layer and the cathode electrode layer, the first        electron transport layer is in direct contact with the second        electron transport layer, and wherein the first electron        transport layer is arranged nearer to the emission layer and the        second electron transport layer is arranged nearer to the        cathode electrode layer; and wherein the second electron        transport layer comprises a non-emitter dopant and comprises:    -   ≥50 wt.-% to ≤95 wt.-%, preferably ≥60 wt.-% to ≤90 wt.-%, and        more preferred ≥70 wt.-% to ≤90 wt.-%, and most preferred about        80 wt.-%. of i) the first organic aromatic matrix compound; and    -   ≥5 wt.-% to ≤50 wt.-%, preferably ≥10 wt.-% to ≤40 wt.-%, and        more preferred ≥10 wt.-% to ≤30 wt.-%, and most preferred about        20 wt.-%, of ii) the polar organic aromatic phosphine compound;        wherein the wt.-% is based on the total weight of i) and ii) of        the second electron transport layer.

Electron Transport Layer Stack

The electron transport layer stack according to the invention, comprisesat least two electron transport layers, wherein

a) the first electron transport layer comprises i) a first organicaromatic matrix compound having a MW of about ≥400 to about ≤1000 and adipole moment of about ≥0 Debye and about ≤2.5 Debye, wherein the firstelectron transport layer is free of a polar organic aromatic phosphinecompound; and

b) the second electron transport layer comprises two organic aromaticmatrix compounds, which are a mixture of:

-   -   i) the first organic aromatic matrix compound; and    -   ii) a polar organic aromatic phosphine compound having a MW of        about ≥400 to about ≤1000, and a dipole moment of about >2.5        Debye and about ≤10 Debye.

According to another aspect the second electron transport layer maycomprises i) the first organic aromatic matrix compound and ii) a polarorganic aromatic phosphine compound having a MW of about ≥400 to about≤1000, and a dipole moment of about >2.5 Debye and about ≤10 Debye,preferably of about ≥3 and ≤5 Debye, even more preferred ≥2.5 and lessthan ≤4 Debye.

The use of a first organic aromatic matrix compound and a polar organicaromatic phosphine compound having a MW of about ≥400 to about ≤1000offers the benefit of good control of the deposition rate during vacuumthermal evaporation and high reproducibility in manufacturing processes.If the MW is less than 400, the deposition rate cannot be controlled asthe evaporation rate is too high. If the MW is above 1000, thedeposition rate cannot be controlled as the evaporation rate is too low.

If the first organic aromatic matrix compound has a dipole moment of ≥0and ≤2.5 Debye, very efficient electron transport is achieved and theOLED can be operated at very low operating voltages and/or high externalquantum efficiency EQE and/or very long lifetime are obtained.

The use of a polar organic aromatic phosphine compound having a dipolemoment of about >2.5 Debye and about ≤10 Debye, offers the benefit ofefficient electron injection from the cathode and/or electron injectionlayer and efficient electron transport into the first electron transportlayer.

Another advantage of the electron transport layer stack according to thepresent invention is that injection and transport of electrons may bebalanced and holes may be efficiently blocked. In a conventional OLED,since the amounts of electrons and holes vary with time, after drivingis initiated, the number of excitons generated in an emission area maybe reduced. As a result, a carrier balance may not be maintained, so asto reduce the lifetime of the OLED.

In a preferred embodiment, the triplet level T1 of the first organicaromatic matrix compound is selected lower than the triplet level T1 ofthe polar organic aromatic phosphine compound, preferably T1 of thefirst organic matrix compound is at least 0.1 eV lower, more preferablyat least 0.2 eV lower than the triplet level T1 of the polar organicaromatic phosphine compound.

According to various aspects, the reduction potential of the firstorganic matrix compound is less negative than the reduction potential ofthe polar organic aromatic phosphine compound.

According to various aspects, the LUMO of the first organic matrixcompound is more negative than the LUMO of the polar organic aromaticphosphine compound.

If the organic aromatic matrix compound and the polar organic aromaticphosphine compound are selected in this range, very low operatingvoltage and/or high external quantum efficiency and/or long lifetime areobtained, as the charge balance can be maintained during operation ofthe OLED.

The present invention offers a significant benefit in terms of takt timeand yield, as the layers can be rapidly deposited while the VTE (vacuumthermal evaporation) sources move back and forth underneath thesubstrate.

In a preferred embodiment, the first VTE source containing the firstorganic aromatic matrix compound moves first underneath the substrateand the first electron transport layer is deposited onto the emissionlayer. The shutter of the second VTE source containing the polar organicaromatic phosphine compound stays closed. Then, the shutter is opened onthe second VTE source and the second electron transport layer isdeposited while the first and second VTE source move backwardsunderneath the substrate. If a non-emitter dopant is deposited at thesame time as the polar organic aromatic phosphine compound, the shutterof a third VTE source is opened and closed at the same time as theshutter of the second VTE source.

In another preferred embodiment, the shutter of the first, second andoptional third VTE source are open while the third electron transportlayer (163) is deposited onto the emission layer. Then the shutter isclosed on the second and third VTE source and the shutter stays open onthe first VTE source, while the sources move backwards underneath thesubstrate to deposit the first electron transport layer (161). Then, theshutters of the second and optional third VTE source are opened againand the first, second and third VTE source move forwards to deposit thesecond electron transport layer (162). Thereby, alternating layers offirst and second electron transport layer may be rapidly deposited tillthe desired layer thickness is obtained.

Preferably, the first organic aromatic matrix compound in the firstelectron transport layer and the first organic aromatic matrix compoundin the second electron transport layer are selected the same compound.More preferred, the first organic aromatic matrix compound in all layersof the ETL-stack is selected the same compound.

According to another aspect, the electron transport layer stack is freeof an emitter dopant which emits visible light at operation of the OLED.

According to another aspect, the first electron transport layer is freeof a non-emitter dopant and the second electron transport layercomprises a non-emitter dopant, wherein the non-emitter dopant is ametal compound, preferably the metal compound is selected from the groupcomprising a metal halide, a metal organic complex and/or a zero-valentmetal.

The electron transport layer stack is arranged between the emissionlayer and the electron cathode layer. The electron transport layer stackcan be arranged between the emission layer and the electron injectionlayer, if the OLED comprises an injection layer.

Preferably, the ETL-stack is contacting sandwiched between the emissionlayer and electron injection layer.

In another preferred embodiment, the ETL-stack is contacting sandwichedbetween the emission layer and the cathode electrode.

In another embodiment, the electron transport layer may be contactingsandwiched between a hole blocking layer and an electron injectionlayer, if the OLED comprises a hole blocking layer and an injectionlayer.

According to various embodiments of the OLED of the present inventionthe electron transport layer stack comprises at least two electrontransport layers, wherein

-   a) the first electron transport layer comprises i) a first organic    aromatic matrix compound having a MW of about ≥400 to about ≤1000    and a dipole moment of about ≥0 Debye and about ≤2.5 Debye, wherein    the first electron transport layer is free of a polar organic    aromatic phosphine compound; and-   b) the second electron transport layer comprises two organic    aromatic matrix compounds, which are a mixture of:    -   i) the first organic aromatic matrix compound; and    -   ii) a polar organic aromatic phosphine compound having a MW of        about ≥400 to about ≤1000, and a dipole moment of about >2.5        Debye and about ≤10 Debye.

The organic light emitting device may comprise further electrontransport layers, preferably a third and optional a fourth electrontransport layer. The first, second, third and fourth electron transportlayer may form an electron transport layer stack, wherein the firstelectron transport layer is in direct contact with the second electrontransport layer, the second electron transport layer is in directcontact with the third electron transport layer, and the third electrontransport layer is in direct contact with the fourth electron transportlayer. As an alternative embodiment the first and second electrontransport layer forms a separate electron transport layer stack, and thethird and optional fourth electron transport layer forms a separateelectron transport layer stack and may be arranged between a chargegeneration layer and the cathode.

According to another aspect the OLED may comprises an electron transportlayer stack of a first electron transport layer, a second electrontransport layer, a third electron transport layer, and a fourth electrontransport layer, wherein the fourth electron transport layer comprises afirst organic aromatic matrix compound having a MW of about ≥400 toabout ≤1000 and a dipole moment of about ≥0 Debye and about ≤2.5 Debye,wherein the fourth electron transport layer is free of a polar organicaromatic phosphine compound.

Preferably, the first electron transport layer and fourth electrontransport layer may be selected the same, and the second and thirdelectron transport layer may be selected the same.

According to a more preferred aspect there is provided an organic lightemitting diode (OLED) wherein the organic light emitting diode comprisesan electron transport layer stack of a first electron transport layer, asecond electron transport layer and a third electron transport layer,wherein the third electron transport layer is arranged nearest to theanode, the second electron transport layer is arranged nearest to thecathode and the first electron transport layer is arranged in betweenthe third electron transport layer and the second electron transportlayer.

According to a more preferred aspect there is provided an organic lightemitting diode (OLED) wherein the organic light emitting diode comprisesan electron transport layer stack of a first electron transport layer, asecond electron transport layer and a third electron transport layer,wherein the third electron transport layer is arranged nearest to theanode, the second electron transport layer is arranged nearest to thecathode and the first electron transport layer is arranged in betweenthe third electron transport layer and the second electron transportlayer, and wherein the third electron transport layer comprises twoorganic aromatic matrix compounds, which are a mixture of:

-   i) a first organic aromatic matrix compound having a MW of about    ≥400 to about ≤1000 and a dipole moment of about ≥0 Debye and about    ≤2.5 Debye and which is free of a polar organic aromatic phosphine    compound; and-   ii) a polar organic aromatic phosphine compound having a MW of about    ≥400 to about ≤1000 and a dipole moment of about >2.5 Debye and    about ≤10 Debye, and-   iii) optional a non-emitter dopant, wherein the non-emitter dopant    is a metal compound, preferably the metal compound is selected from    the group comprising an metal halide, metal organic complex and/or    zero-valent metal.

According to a further aspect there is provided an organic lightemitting diode (OLED) wherein the organic light emitting diode comprisesan electron transport layer stack of a first electron transport layer, asecond electron transport layer, a third electron transport layer and afourth electron transport layer, wherein the third electron transportlayer is arranged nearest to the anode, followed by the first electrontransport layer, followed by the second electron transport layer andfollowed by the fourth electron transport layer, wherein the fourthelectron transport layer is arranged nearest to the cathode and thefirst electron transport layer and second electron transport layer arearranged in between the third electron transport layer and the fourthelectron transport layer.

According to another aspect there is provided an organic light emittingdiode (OLED) wherein the organic light emitting diode comprises anelectron transport layer stack of a first electron transport layer and asecond electron transport layer, and an electron layer stack of a thirdelectron transport layer and a fourth electron transport layer, whereinthe third electron transport layer is arranged nearest to the cathodeand the fourth electron transport layer contacts the third electrontransport layer is arranged nearest to the anode; and wherein the secondelectron transport layer is arranged nearest to the cathode and thefirst electron transport layer contacts the second electron transportlayer and is arranged nearest to the anode.

According to a more preferred aspect there is provided an organic lightemitting diode (OLED) wherein the organic light emitting diode comprisesan electron transport layer stack of a first electron transport layer, asecond electron transport layer, a third electron transport layer and afourth electron transport layer, wherein the third electron transportlayer is arranged nearest to the anode, followed by the first electrontransport layer, followed by the second electron transport layer andfollowed by the fourth electron transport layer, wherein the fourthelectron transport layer is arranged nearest to the cathode and thefirst electron transport layer and second electron transport layer arearranged in between the third electron transport layer and the fourthelectron transport layer, and wherein the third electron transport layercomprises two organic aromatic matrix compounds, which are a mixture of:

-   i) a first organic aromatic matrix compound having a MW of about    ≥400 to about ≤1000 and a dipole moment of about ≥0 Debye and about    ≤2.5 Debye and which is free of a polar organic aromatic phosphine    compound; and-   ii) a polar organic aromatic phosphine compound having a MW of about    ≥400 to about ≤1000 and a dipole moment of about >2.5 Debye and    about ≤10 Debye, and-   iii) optional a non-emitter dopant, wherein the non-emitter dopant    is a metal compound, preferably the metal compound is selected from    the group comprising an metal halide, metal organic complex and/or    zero-valent metal; and wherein    the fourth electron transport layer comprises:    -   a first organic aromatic matrix compound having a MW of about        ≥400 to about ≤1000 and a dipole moment of about ≥0 Debye and        about ≤2.5 Debye, wherein the fourth electron transport layer is        free of a polar organic aromatic phosphine compound.

According to a more preferred aspect, there is provided an organic lightemitting diode (OLED) wherein the organic light emitting diodecomprises:

-   -   at least one anode electrode;    -   at least one emission layer, wherein the emission layer        comprises at least one emitter dopant that emits visible light        at operation of the OLED (100);    -   at least one cathode electrode layer;    -   an electron transport layer stack of a first electron transport        layer (161), a second electron transport layer (162) and a third        electron transport layer (163), wherein the third electron        transport layer (163) comprises two organic aromatic matrix        compounds, which are a mixture of:

-   i) a first organic aromatic matrix compound having a MW of about    ≥400 to about ≤1000 and a dipole moment of about ≥0 Debye and about    ≤2.5 Debye and which is free of a polar organic aromatic phosphine    compound; and

-   ii) a polar organic aromatic phosphine compound having a MW of about    ≥400 to about ≤1000 and a dipole moment of about >2.5 Debye and    about ≤10 Debye, and

-   iii) optional a non-emitter dopant, wherein the non-emitter dopant    is a metal compound, preferably the metal compound is selected from    the group comprising an metal halide, metal organic complex and/or    zero-valent metal.

In a preferred embodiment, the second electron transport layer (162) andthe third electron transport layer (163) may have the same composition.

According to a more preferred aspect, there is provided an organic lightemitting diode (OLED) wherein the organic light emitting diodecomprises, wherein the OLED comprises an electron transport layer stack(160) of a first electron transport layer (161), a second electrontransport layer (162), a third electron transport layer (163), and afourth electron transport layer (164), wherein the fourth electrontransport layer (164) comprises:

-   -   a first organic aromatic matrix compound having a MW of about        ≥400 to about ≤1000 and a dipole moment of about ≥0 Debye and        about ≤2.5 Debye, wherein the fourth electron transport layer        (161) is free of a polar organic aromatic phosphine compound.

In another aspect is provided an electron transport layer stackcomprises five or more electron transport layers, wherein an electrontransport layer comprises i) a first organic aromatic matrix compoundhaving a MW of about ≥400 to about ≤1000 and a dipole moment of about ≥0Debye and about ≤2.5 Debye, wherein the first electron transport layeris free of a polar organic aromatic phosphine compound; and an electrontransport layer comprises two organic aromatic matrix compounds, whichare a mixture of i) the first organic aromatic matrix compound; and ii)a polar organic aromatic phosphine compound having a MW of about ≥400 toabout ≤1000, and a dipole moment of about >2.5 Debye and about ≤10 Debyeare alternatingly arranged.

In a preferred embodiment, the first electron transport layer (161) andthe fourth electron transport layer (164) may have the same composition.

In a more preferred embodiment, the second electron transport layer(162) and the third electron transport layer (163) may have the samecomposition and the first electron transport layer (161) and the fourthelectron transport layer (164) may have the same composition.

Preferably, the second and optional third electron transport layeraccording to the invention comprises a polar organic aromatic phosphineoxide compound.

In a preferred embodiment of the OLED, the electron transport layerstack is free of emitter compounds, also named emitter dopants, whichemit visible light at operation of the OLED.

According to another aspect, the electron transport layer stack can befree of a metal, metal halide, metal salt and/or lithium organic metalcomplex.

The thickness of the first electron transport layer may be in the rangeof ≥2 nm to about ≤10 nm, preferably ≥3 nm to about ≤5 nm.

The thickness of the second electron transport layer may be in the rangeof ≥20 nm to about ≤50 nm, preferably ≥25 nm to about ≤40 nm.

According to various embodiments of the OLED of the present inventionthe thicknesses of the electron transport layer stack can be in therange of about ≥20 nm to about ≤100 nm, preferably of about ≥30 nm toabout ≤80 nm, further preferred of about ≥35 nm to about ≤60 nm, andmore preferred of about ≥33 nm to about ≤40 nm.

The electron transport layer of the ETL-stack may be formed on the EMLby vacuum deposition, spin coating, slot-die coating, printing, casting,or the like. When the electron transport layer of the ETL-stack areformed by vacuum deposition or spin coating, the deposition and coatingconditions may be similar to those for formation of the HIL. However,the deposition and coating conditions may vary, according to a compoundthat is used to form the electron transport layers of the ETL-stack.

First Organic Aromatic Matrix Compound

According to one embodiment, the first organic aromatic matrixcompound/s have a MW of about ≥400 to about ≤1000 and a dipole moment ofabout ≥0 Debye and about ≤2.5 Debye. When the first organic aromaticmatrix compound has a MW in this range, the evaporation rate may becontrolled to a level sufficient for manufacturing and high takt timecan be realized while maintaining high reproducibility.

Particularly high external quantum efficiency EQE, low operating voltageand/or lifetime are obtained when the first organic matrix compound hasa dipole moment≥0 and ≤2.5 Debye. When the first organic aromatic matrixcompound has a dipole moment in this range, it can also be described asnon-polar matrix compound.

The dipole moment |{right arrow over (μ)}| of a molecule containing Natoms is given by:

$\overset{\rightarrow}{\mu} = {\sum\limits_{i}^{N}{q_{i}\overset{\rightarrow}{r_{\iota}}}}$${\overset{\rightarrow}{\mu}} = \sqrt{\mu_{x}^{2} + \mu_{y}^{2} + \mu_{z}^{2}}$

where q_(i) and {right arrow over (r_(l))} are the partial charge andposition of atom i in the molecule. The dipole moment is determined by asemi-empirical molecular orbital method. The values in Table 2 werecalculated using the method as described below. The partial charges andatomic positions are obtained using either the DFT functional of Beckeand Perdew BP with a def-SV(P) basis or the hybrid functional B3LYP witha def2-TZVP basis set as implemented in the program package TURBOMOLEV6.5. If more than one conformation is viable, the conformation with thelowest total energy is selected to determine the dipole moment.

When the first organic aromatic matrix compound has a dipole momentbetween 0 and 2.5 Debye, the first organic aromatic matrix compound maycontain a center of inversion I, a horizontal mirror plane, more thanone C_(n) axis (n>1), and/or n C₂ perpendicular to C_(n).

The first organic aromatic matrix compound is an electron transportingcompound. Therefore, the triplet level T₁ of the first organic matrixcompound may be selected in the range which supports electron transport.Preferably, the first organic aromatic matrix compound is selected froman organic aromatic matrix compound with a triplet level>1 eV and <2.9eV, preferably >1.2 and <2.8 eV, more preferred >1.3 and <2.7 eV.

The triplet level T₁ is determined through quantum-chemicalcalculations. To this end, the software package “Gaussion-03 W” is used.Firstly a geometry optimisation is carried out using the “GroundState/Semi-empirical/Default Spin/AMI/Charge 0/Spin Singlet” method.This is followed by an energy calculation on the basis of the optimisedgeometry. This is followed by an energy calculation on the basis of theoptimised geometry. The “TD-SFC/DFT/Default Spin/B3PW91” method with the“6-31G(d)” base set is used (Charge 0, Spin Singlet). The result may befurther optimized using B3PW91.

According to various aspects, the reduction potential of the firstorganic matrix compound is less negative when measured under the sameconditions with cyclic voltammetry in tetrahydrofurane against Fc+/Fcredox couple than the reduction potential of pyrene, preferably lessnegative than the reduction potential of1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene, more preferably lessnegative than the reduction potential of(9-phenyl-9H-carbazole-2,7-diyl)bis(diphenylphosphine oxide) and morenegative than the reduction potential of4,4′-bis(4,6-diphenyl-1,3,5-triazin-2-yl)biphenyl, preferably morenegative than the reduction potential of4-(naphtalen-1-yl)-2,7,9-triphenylpyrido[3,2-h]quinazoline.

The redox potential is determined by cyclic voltammetry withpoteniosttic device Metrohm PGSTAT30 and software Metrohm Autolab GPESat room temperature. The redox potentials given at particular compoundswere measured in an argon de-aerated, dry 0.1M THF solution of thetested substance, under argon atmosphere, with 0.1M tetrabutylammoniumhexafluorophosphate supporting electrolyte, between platinum workingelectrodes and with an Ag/AgCl pseudo-standard electrode (Metrohm Silverrod electrode), consisting of a silver wire covered by silver chlorideand immersed directly in the measured solution, with the scan rate 100mV/s. The first run was done in the broadest range of the potential seton the working electrodes, and the range was then adjusted withinsubsequent runs appropriately. The final three runs were done with theaddition of ferrocene (in 0.1M concentration) as the standard. Theaverage of potentials corresponding to cathodic and anodic peak of thestudied compound, after subtraction of the average of cathodic andanodic potentials observed for the standard Fc+/Fc redox couple,afforded finally the values reported above. All studied compounds aswell as the reported comparative compounds showed well-definedreversible electrochemical behaviour.

Under these conditions, the reduction potential of pyrene is −2.64 V,the reduction potential of1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene is −2.58 V, thereduction potential of(9-phenyl-9H-carbazole-2,7-diyl)bis(diphenylphosphine oxide) is −2.51 V,the reduction potential of4,4′-bis(4,6-diphenyl-1,3,5-triazin-2-yl)biphenyl is −2.03 V, and thereduction potential of4-(naphtalen-1-yl)-2,7,9-triphenylpyrido[3,2-h]quinazoline is −2.18 V.

A simple rule is very often used for the conversion of redox potentialsinto electron affinities and ionization potential: IP (in eV)=4.84eV+e*Eox (wherein Eox is given in Volt vs. ferrocene/ferrocenium(Fc/Fc+) and EA (in eV)=4.84 eV+e*Ered (Ered is given in Volt vs.Fc/Fc+) respectively (see B. W. D'Andrade, Org. Electron. 6, 11-20(2005)), e* is the elemental charge. It is common practice, even if notexactly correct, to use the terms “energy of the HOMO” E(HOMO) and“energy of the LUMO” E(LUMO), respectively, as synonyms for theionization energy and electron affinity (Koopmans Theorem).

Thereby, the LUMO of pyrene is −2.2 eV, the LUMO of1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene is −2.26 eV, the LUMOof (9-phenyl-9H-carbazole-2,7-diyl)bis(diphenylphosphine oxide) is −2.33eV, the LUMO of 4,4′-bis(4,6-diphenyl-1,3,5-triazin-2-yl)biphenyl is−2.81 eV, and the LUMO of4-(naphtalen-1-yl)-2,7,9-triphenylpyrido[3,2-h]quinazoline is −2.66 eV.

According to a more preferred aspect, the first organic aromatic matrixcompound may comprises a conjugated system of at least ten, preferablyat least fourteen delocalized electrons.

Examples of conjugated systems of delocalized electrons are systems ofalternating pi- and sigma bonds. Optionally, one or more two-atomstructural units having the pi-bond between its atoms can be replaced byan atom bearing at least one lone electron pair, typically by a divalentatom selected from O, S or Se or by a trivalent atom selected from N orP. Preferably, the conjugated system of delocalized electrons comprisesat least one aromatic or heteroaromatic ring according to the Hückelrule. Also preferably, the first organic aromatic matrix compound maycomprise at least two aromatic or heteroaromatic rings which are eitherlinked by a covalent bond or condensed.

According to a more preferred aspect, the first organic aromatic matrixcompound is selected from the group comprising benzo[k]fluoranthene,pyrene, anthracene, fluorene, spiro(bifluorene), phenanthrene, perylene,triptycene, spiro[fluorene-9,9′-xanthene], coronene, triphenylene,xanthene, benzofurane, dibenzofurane, dinaphthofurane, acridine,benzo[c]acridine, dibenzo[c,h]acridine, dibenzo[a,j]acridine, triazine,pyridine, pyrimidine, carbazole, thienopyrimidine, dithienothiophene,benzothienopyrimidine, benzothieno-pyrimidine, triaryl borane ormixtures thereof.

According to a more preferred aspect, the first organic aromatic matrixcompound is free of a phosphine group, a phenanthroline group, abenzimidazole group or metal cations.

It may be further preferred that the first organic aromatic matrixcompound comprises a triaryl borane compound of formula (1)

wherein R¹, R³ and R⁷ are independently selected from a group consistingof H, D, C₁-C₁₆ alkyl and C₁-C₁₆ alkoxy;R², R⁵ and R⁶ are independently selected from a group consisting of H,D, C₁-C₁₆ alkyl, C₁-C₁₆ alkoxy and C₆-C₂₀ aryl;Ar⁰ is selected from substituted or unsubstituted C₆-C₂₀ aryl, wherein,in case that Ar⁰ is substituted, the substituents are independentlyselected from a group consisting of D, C₁-C₁₂ alkyl, C₁-C₁₆ alkoxy andC₆-C₂₀ aryl; andAr¹ is selected from substituted or unsubstituted C₆-C₂₀ arylene,wherein, in case that Ar¹ is substituted, the substituents areindependently selected from a group consisting of D, C₁-C₁₂ alkyl,C₁-C₁₆ alkoxy and C₆-C₂₀ aryl; andAr² is selected from Ar² is selected from a group consisting of H, D,substituted or unsubstituted C₆-C₄₀ aryl and C₅-C₄₀ heteroaryl.

Preferably, Ar⁰ is selected from substituted or unsubstituted phenyl ornaphthyl, wherein, in case that Ar⁰ is substituted, the substituents areindependently selected from a group consisting of D, C₁-C₁₂ alkyl,C₁-C₁₆ alkoxy and C₆-C₂₀ aryl.

Triaryl borane compounds of formula (1):

are disclosed in WO2015049030A2 and EP15187135.7.

In a further preferred embodiment, the first organic aromatic matrixcompound comprises: a dibenzo[c,h]acridine compound of formula (2)

and/or a dibenzo[a,j]acridine compound of formula (3)

and/or a benzo[c]acridine compound of formula (4)

wherein Ar³ is independently selected from C₆-C₂₀ arylene, preferablyphenylene, biphenylene, or fluorenylene;

Ar⁴ is independently selected from unsubstituted or substituted C₆-C₄₀aryl, preferably phenyl, naphthyl, anthranyl, pyrenyl, or phenanthryl;

and in case that Ar⁴ is substituted, the one or more substituents may beindependently selected from the group consisting of C₁-C₁₂ alkyl andC₁-C₁₂ heteroalkyl, wherein C₁-C₅ alkyl is preferred.

Suitable dibenzo[c,h]acridine compounds are disclosed in EP 2 395 571.Suitable dibenzo[a,j]acridine are disclosed in EP 2 312 663. Suitablebenzo[c]acridine compounds are disclosed in WO 2015/083948.

In a further embodiment, it is preferred that the first organic aromaticmatrix compound comprises a dibenzo[c,h]acridine compound substitutedwith C₆-C₄₀ aryl, C₅-C₄₀ heteroaryl and/or C₁-C₁₂ alkyl groups,preferably 7-(naphthalen-2-yl)dibenzo[c,h]acridine,7-(3-(pyren-1-yl)phenyl)dibenzo[c,h]acridine,7-(3-(pyridin-4-yl)phenyl)dibenzo[c,h]acridine.

In a further embodiment, it is preferred that the first organic aromaticmatrix compound comprises a dibenzo[a,j]acridine compound substitutedwith C₆-C₄₀ aryl, C₅-C₄₀ heteroaryl and/or C₁-C₁₂ alkyl groups,preferably 14-(3-(pyren-1-yl)phenyl)dibenzo [a,j]acridine.

In a further embodiment, it is preferred that the first organic aromaticmatrix compound comprises a benzo[c]acridine compound substituted withC₆-C₄₀ aryl, C₅-C₄₀ heteroaryl and/or C₁-C₁₂ alkyl groups, preferably7-(3-(pyren-1-yl)phenyl)benzo[c]acridine.

It may be further preferred that the first organic aromatic matrixcompound comprises a triazine compound of formula (5)

wherein Ar⁵ is independently selected from unsubstituted or substitutedC₆-C₂₀ aryl or Ar^(5.1)-Ar^(5.2),

wherein Ar^(5.1) is selected from unsubstituted or substituted C₆-C₂₀arylene and

Ar^(5.2) is selected from unsubstituted or substituted C₆-C₂₀ aryl orunsubstituted and substituted C₅-C₂₀ heteroaryl;

Ar⁶ is selected from unsubstituted or substituted C₆-C₂₀ arylene,preferably phenylene, biphenylene, terphenylene, fluorenylene;

Ar⁷ is independently selected from a group consisting of substituted orunsubstituted aryl, substituted or unsubstituted heteroaryl, the aryland the heteroaryl having 6 to 40 ring-forming atoms, preferably phenyl,naphthyl, phenantryl, fluorenyl, terphenyl, pyridyl, quinolyl,pyrimidyl, triazinyl, benzo[h]quinolinyl, orbenzo[4,5]thieno[3,2-d]pyrimidine;

x is selected from 1 or 2,

wherein in case that Ar⁵ is substituted the one or more substituents mayindependently be selected from C₁-C₁₂ alkyl and C₁-C₁₂ heteroalkyl,preferably C₁-C₅ alkyl;

and in case that Ar⁷ is substituted, the one or more substituents may beindependently selected from C₁-C₁₂ alkyl and C₁-C₁₂ heteroalkyl,preferably C₁-C₅ alkyl, and from C₆-C₂₀ aryl.

Suitable triazine compounds are disclosed in US 2011/284832, WO2014/171541, WO 2015/008866, WO2015/105313, JP 2015-074649 A, JP2015-126140, KR 2015/0088712, KR2015-012551 and WO16171358A1.

Furthermore, it is preferred that the first organic aromatic matrixcompound comprises a triazine compound substituted with C₆-C₄₀ aryl,C₅-C₄₀ heteroaryl and/or C₁-C₁₂ alkyl groups, preferably3-[4-(4,6-di-2-naphthalenyl-1,3,5-triazin-2-yl)phenyl]quinolone,2-[3-(6′-methyl[2,2′-bipyridin]-5-yl)-5-(9-phenanthrenyl)phenyl]-4,6-diphenyl-1,3,5-triazine,2-(3-(phenanthren-9-yl)-5-(pyridin-2-yl)phenyl)-4,6-diphenyl-1,3,5-triazine,2,4-diphenyl-6-(5′″-phenyl-[1,1′:3′,1″:3″,1′″:3′″,1″″-quinquephenyl]-3-yl)-1,3,5-triazine,2-([1,1′-biphenyl]-3-yl)-4-(3′-(4,6-diphenyl-1,3,5-triazin-2-yl)-[1,1′-biphenyl]-3-yl)-6-phenyl-1,3,5-triazineand/or2-(3′-(4,6-diphenyl-1,3,5-triazin-2-yl)-[1,1′-biphenyl]-3-yl)-4-phenylbenzo[4,5]thieno[3,2-d]pyrimidine.

In a preferred embodiment, the first organic aromatic matrix compoundcomprises a benzothienopyrimidine compound substituted with C₆-C₄₀aryl,C₅-C₄₀ heteroaryl and/or C₁-C₁₂ alkyl groups, preferably2-phenyl-4-(4′,5′,6′-triphenyl-[1,1′:2′,1″:3″,1′″-quaterphenyl]-3′″-yl)benzo[4,5]thieno[3,2-d]pyrimidine.Suitable benzothienopyrimidine compounds are disclosed in W2015/0105316.

In a preferred embodiment, the first organic aromatic matrix compoundcomprises a benzo[k]fluoranthene compound substituted with C₆-C₄₀aryl,C₅-C₄₀ heteroaryl and/or C₁-C₁₂ alkyl groups, preferably 7,12-diphenylbenzo[k]fluoranthene. Suitable benzo[k]fluoranthene compoundsare disclosed in JP10189247 A2.

In a preferred embodiment, the first organic aromatic matrix compoundcomprises a perylene compound substituted with C₆-C₄₀ aryl, C₆-C₄₀heteroaryl and/or C₁-C₁₂ alkyl groups, preferably3,9-bis([1,1′-biphenyl]-2-yl)perylene, 3,9-di(naphthalene-2-yl)peryleneor 3,10-di(naphthalene-2-yl)perylene. Suitable perylene compounds aredisclosed in US2007202354.

In a preferred embodiment, the first organic aromatic matrix compoundcomprises a pyrene compound. Suitable pyrene compounds are disclosed inUS20050025993.

In a preferred embodiment, the first organic aromatic matrix compoundcomprises a spiro-fluorene compound. Suitable spiro-fluorene compoundsare disclosed in JP2005032686.

In a preferred embodiment, the first organic aromatic matrix compoundcomprises a xanthene compound. Suitable xanthene compounds are disclosedin US2003168970A and WO 2013149958.

In a preferred embodiment, the first organic aromatic matrix compoundcomprises a coronene compound. Suitable coronene compounds are disclosedin Adachi, C.; Tokito, S.; Tsutsui, T.; Saito, S., Japanese Journal ofApplied Physics, Part 2: Letters (1988), 27(2), L269-L271.

In a preferred embodiment, the first organic aromatic matrix compoundcomprises a triphenylene compound. Suitable triphenylene compounds aredisclosed in US20050025993.

In a preferred embodiment, the first organic aromatic matrix compound isselected from carbazole compounds. Suitable carbazole compounds aredisclosed in US2015207079.

In a preferred embodiment, the first organic aromatic matrix compound isselected from dithienothiophene compounds. Suitable dithienothiophenecompounds are disclosed in KR2011085784.

In a preferred embodiment, the first organic aromatic matrix compoundcomprises an anthracene compound. Particularly preferred are anthracenecompounds represented by Formula 400 below:

In Formula 400, Ar₁₁₁ and Ar₁₁₂ may be each independently a substitutedor unsubstituted C₆-C₆₀ arylene group; Ar₁₁₃ to Ar₁₁₆ may be eachindependently a substituted or unsubstituted C₁-C₁₀ alkyl group or asubstituted or unsubstituted C₆-C₆₀ aryl group; and g, h, i, and j maybe each independently an integer from 0 to 4.

In some embodiments, Ar₁₁₁ and Ar₁₁₂ in Formula 400 may be eachindependently one of:

a phenylene group, a naphthylene group, a phenanthrenylene group, or apyrenylene group, or a phenylene group, a naphthylene group, aphenanthrenylene group, a fluorenyl group, or a pyrenylene group, eachsubstituted with at least one of a phenyl group, a naphthyl group, or ananthryl group.

In Formula 400, g, h, i, and j may be each independently an integer of0, 1, or 2.

In Formula 400, Ar₁₁₃ to Ar₁₁₆ may be each independently one of a C₁-C₁₀alkyl group substituted with at least one of a phenyl group, a naphthylgroup, or an anthryl group;

a phenyl group, a naphthyl group, an anthryl group, a pyrenyl group, aphenanthrenyl group, or a fluorenyl group;

a phenyl group, a naphthyl group, an anthryl group, a pyrenyl group, aphenanthrenyl group, or a fluorenyl group, each substituted with atleast one of a deuterium atom, a halogen atom, a hydroxyl group, a cyanogroup, a nitro group, an amino group, an amidino group, a hydrazinegroup, a hydrazone group, a carboxyl group or a salt thereof, a sulfonicacid group or a salt thereof, a phosphoric acid group or a salt thereof,a C₁-C₆₀ alkyl group, a C₂-C₆₀ alkenyl group, a C₂-C₆₀ alkynyl group, aC₁-C₆₀ alkoxy group, a phenyl group, a naphthyl group, an anthryl group,a pyrenyl group, a phenanthrenyl group, or a fluorenyl group; or havingthe following structure

According to a further more preferred aspect the first organic aromaticmatrix compound can be selected from a compound of Table 1 below. Thesehave been found to have a particularly beneficial effect on operatingvoltage, external quantum efficiency and/or lifetime.

TABLE 1 First organic aromatic matrix compounds with a dipole moment ≥0Debye and ≤2.5 Debye which may be suitable used Referred to as:Structure ADN

ETM1-1

ETM1-2

ETM1-3

ETM1-4

ETM1-5

ETM1-6

ETM1-7

ETM1-8

ETM1-9

ETM1-10

ETM1-11

ETM1-12

ETM1-13

ETM1-14

ETM1-15

ETM1-16

ETM1-17

ETM1-18

ETM1-19

ETM1-20

ETM1-21

ETM1-22

ETM1-23

ETM1-24

ETM1-25

ETM1-26

ETM1-27

ETM1-28

ETM1-29

ETM1-30

ETM1-31

ETM1-32

ETM1-33

ETM1-34

ETM1-35

ETM1-36

ETM1-37

Table 2 below shows the dipole moments of representative examples of thefirst organic aromatic matrix compound with a dipole moment≥0 Debye and≤2.5 Debye.

TABLE 2 Dipole moment/ Reference Name Structure Debye ADN9,10-di(naphthalen-2- yl)anthracene

0.01 ETM1-2 Tri(naphthalen-1-yl)borane

0.14 ETM1-8 bis(2-methylnaphthalen-1- yl)(3-(phenanthren-9-yl)phenyl)borane

0.18 ETM1-15 7-(3-(pyren-1-yl) phenyl)dibenzo[c,h]acridine

1.80 ETM1-17 7-(3-(pyridin-4-yl) phenyl)dibenzo[c,h]acridine

2.26 ETM1-18 14-(3-(pyren-1-yl) phenyl)dibenzo[a,j]acridine

2.50 ETM1-21 7-(3-(pyren-1- yl)phenyl)benzo[c]acridine

2.13 ETM1-29 2-(3-(phenanthren-9-yl)-5- (pyridin-2-yl)phenyl)-4,6-diphenyl-1,3,5-triazine

1.76 ETM1-28 2,4-diphenyl-6-(5′′′-phenyl-[1,1′:3′,1″:3″,1′′′:3′′′,1′′′′- quinquephenyl]-3-yl)-1,3,5- triazine

0.23 ETM1-26 2-([1,1′-biphenyl]-3-yl)-4-(3′-(4,6-diphenyl-1,3,5-triazin-2- yl)-[1,1′-biphenyl]-3-yl)-6-phenyl-1,3,5-triazine

0.13 ETM1-27 2-(3′-(4,6-diphenyl-1,3,5- triazin-2-yl)-[1,1′-biphenyl]-3-yl)-4- phenylbenzo[4,5]thieno[3,2- d]pyrimidine

2.0  ETM1-33 2-phenyl-4-(4′,5′,6′-triphenyl- [1,1′:2′,1″:3″,1′′′-quaterphenyl]-3′′′- yl)benzo[4,5]thieno[3,2- d]pyrimidine

1.6  ETM1-34 7,12-diphenyl- benzo[k]fluoranthene (CAS 16391-62-1)

0.13 ETM1-35 3,9-di(naphthalen-2- yl)perylene (CAS 959611- 30-4)

0.12

In another aspect, the first electron transport layer may comprise asecond organic aromatic matrix compound, preferably the second organicaromatic matrix compound is selected from the emitter matrix compoundand/or hole-blocking matrix compound.

Polar Organic Aromatic Phosphine Compounds Examples of polar organicaromatic phosphine compounds are compounds consisting predominantly fromcovalently bound C, H, O, N, S, P and Se, preferably C, H, O, N and P.

According to a more preferred aspect, the polar organic aromaticphosphine compound is free of metal cations.

According to a more preferred aspect, the polar organic aromaticphosphine compound comprises a conjugated system of at least six, morepreferably at least ten delocalized electrons.

Examples of conjugated systems of delocalized electrons are systems ofalternating pi- and sigma bonds. Optionally, one or more two-atomstructural units having the pi-bond between its atoms can be replaced byan atom bearing at least one lone electron pair, typically by a divalentatom selected from O, S or Se, or by a trivalent atom selected from N orP.

Preferably, the conjugated system of delocalized electrons comprises atleast one aromatic or heteroaromatic ring according to the Hückel rule.Also preferably, the polar organic aromatic phosphine compound maycomprise at least two aromatic or heteroaromatic rings which are eitherlinked by a covalent bond or condensed.

According to another aspect, the polar organic aromatic phosphinecompound is an electron transporting compound. To support electrontransport, the polar organic aromatic phosphine compound may be selectedfrom a compound with a triplet level>1 eV and <2.9 eV, preferably >1.2and <2.8 eV, more preferred >1.3 and <2.7 eV.

According to another aspect, the polar organic aromatic phosphinecompound does not participate in electron transport and electrontransport is supported by the first organic aromatic matrix compound.The polar organic aromatic phosphine compound may be selected from acompound with a triplet level<3.5 and >2.7 eV, more preferably <3.2and >2.8 eV, even more preferred <3.5 and >2.9 eV.

According to various aspects, the reduction potential of the polarorganic aromatic phosphine compound when measured under the sameconditions with cyclic voltammetry in tetrahydrofurane against Fe/Fcredox couple is more negative than the reduction potential of9-phenyl-9H-carbazole-2,7-diyl)bis(diphenylphosphine oxide, preferablymore negative than the reduction potential of [1,1′:4′,1″-terphenyl]-3,5-diylbis(diphenylphosphine oxide) and the same orless negative than the reduction potential ofethane-1,2-diylbis(diphenylphosphine oxide), preferably less negativethan the reduction potential of triphenylene.

Under these conditions, the reduction potential of9-phenyl-9H-carbazole-2,7-diyl)bis(diphenylphosphine oxide is −2.51 V,the reduction potential of [1,1′:4′,1″-terphenyl]-3,5-diylbis(diphenylphosphine oxide) is −2.58 V, thereduction potential of ethane-1,2-diylbis(diphenylphosphine oxide) is−3.17 V and the reduction potential of triphenylene is −3.04 V.

The LUMO of 9-phenyl-9H-carbazole-2,7-diyl)bis(diphenylphosphine oxideis −2.33 eV, the LUMO of [1,1′:4′,1″-terphenyl]-3,5-diylbis(diphenylphosphine oxide) is −2.26 eV, theLUMO of ethane-1,2-diylbis(diphenylphosphine oxide) is −1.67 eV and theLUMO of triphenylene is −1.8 eV.

According to another aspect the polar organic aromatic phosphinecompound can be selected from the group of organic phosphine oxidecompound/s, organic thioxophosphine compound/s or organicselenoxophosphine compound/s.

Preferably, the polar aromatic phosphine compound is selected from aphosphine oxide compound.

According to another aspect there is provided an organic light emittingdiode (OLED) wherein the polar organic aromatic phosphine compound ofthe second electron transport layer has the Formula Ia:

wherein:X is selected from O, S, Se;

-   R¹ and R² are independently selected from C₁ to C₁₂ alkyl,    substituted or unsubstituted C₆ to C₂₀ aryl and substituted or    unsubstituted C₅ to C₂₀ heteroaryl; or R¹ and R² are bridged with an    alkene-di-yl group forming with the P atom a substituted or    unsubstituted five, six or seven member ring; and    A¹ is phenyl or selected from Formula (II):

-   -   wherein    -   R³ is selected from C₁ to C₈ alkane-di-yl, substituted or        unsubstituted C₆ to C₂₀ arylene and substituted or unsubstituted        C₅ to C₂₀ heteroarylene; or    -   A¹ is selected from Formula (III)

-   -   -   wherein        -   n is selected from 0 or 1;        -   m is selected from 1 or 2;        -   o is selected from 1 or 2;        -   and m is 1 if o is 2;

-   Ar¹ is selected from substituted or unsubstituted C₆ to C₂₀ arylene    and substituted or unsubstituted C₅ to C₂₀ heteroarylene;

-   Ar² is selected from substituted or unsubstituted C₁₈ to C₄₀ arylene    and substituted or unsubstituted C₁₀ to C₄₀ heteroarylene;

-   R⁴ is selected from H, C₁ to C₁₂ alkyl, substituted or unsubstituted    C₆ to C₂₀ aryl and substituted or unsubstituted C₅ to C₂₀    heteroaryl.

According to another aspect there is provided an organic light emittingdiode (OLED) wherein organic light emitting diode comprising:

-   -   at least one anode electrode;    -   at least one emission layer, wherein the emission layer        comprises at least one emitter dopant that emits visible light        at operation of the OLED;    -   an electron transport layer stack of at least two electron        transport layers, and wherein    -   a) the first electron transport layer comprises i) a first        organic aromatic matrix compound having a MW of about ≥400 to        about ≤1000 and a dipole moment of about ≥0 Debye and about ≤2.5        Debye, wherein the first electron transport layer is free of a        polar organic aromatic phosphine compound; and    -   b) the second electron transport layer comprises two organic        aromatic matrix compounds, which are a mixture of:        -   i) the first organic aromatic matrix compound; and        -   ii) a polar organic aromatic phosphine compound having a MW            of about ≥400 to about ≤1000, and a dipole moment of            about >2.5 Debye and about ≤10 Debye, wherein the polar            organic aromatic phosphine compound has the Formula Ia:

-   -   wherein:    -   X is selected from O, S, Se;    -   R¹ and R² are independently selected from C₁ to C₁₂ alkyl,        substituted or unsubstituted C₆ to C₂₀ aryl and substituted or        unsubstituted C₅ to C₂₀ heteroaryl; or R¹ and R² are bridged        with an alkene-di-yl group forming with the P atom a substituted        or unsubstituted five, six or seven member ring; and    -   A¹ is phenyl or selected from Formula (II):

-   -   wherein    -   R³ is selected from C₁ to C₈ alkane-di-yl, substituted or        unsubstituted C₆ to C₂₀ arylene and substituted or unsubstituted        C₅ to C₂₀ heteroarylene; or    -   A¹ is selected from Formula (III)

-   -   -   wherein        -   n is selected from 0 or 1;        -   m is selected from 1 or 2;        -   o is selected from 1 or 2;        -   and m is 1 if o is 2;

    -   Ar¹ is selected from substituted or unsubstituted C₆ to C₂₀        arylene and substituted or unsubstituted C₅ to C₂₀        heteroarylene;

    -   Ar² is selected from substituted or unsubstituted C₁₈ to C₄₀        arylene and substituted or unsubstituted C₁₀ to C₄₀        heteroarylene;

    -   R⁴ is selected from H, C₁ to C₁₂ alkyl, substituted or        unsubstituted C₆ to C₂₀ aryl and substituted or unsubstituted C₅        to C₂₀ heteroaryl; and

    -   at least one cathode electrode layer; wherein        the electron transport layer stack is arranged between the        emission layer and the cathode electrode layer,        the first electron transport layer is in direct contact with the        second electron transport layer, and wherein        the first electron transport layer is arranged nearer to the        emission layer and the second electron transport        layer is arranged nearer to the cathode electrode layer.

According to another aspect there is provided an organic light emittingdiode (OLED) wherein the polar organic aromatic phosphine compound hasthe Formula Ia:

wherein:X is selected from O, S, Se;

-   R¹ and R² are independently selected from C₁ to C₁₂ alkyl,    substituted or unsubstituted C₆ to C₂₀ aryl and substituted or    unsubstituted C₅ to C₂₀ heteroaryl; or R¹ and R² are bridged with an    alkene-di-yl group forming with the P atom a substituted or    unsubstituted five, six or seven member ring; and    A¹ is phenyl or selected from Formula (II):

-   -   wherein    -   R³ is selected from C₁ to C₈ alkane-di-yl, substituted or        unsubstituted C₆ to C₂₀ arylene and substituted or unsubstituted        C₅ to C₂₀ heteroarylene; or    -   A¹ is selected from Formula (III)

-   -   -   wherein        -   n is selected from 0 or 1;        -   m is selected from 1 or 2;        -   o is selected from 1 or 2;        -   and m is 1 if o is 2;

-   Ar¹ is selected from substituted or unsubstituted C₆ to C₂₀ arylene    and substituted or unsubstituted C₅ to C₂₀ heteroarylene;

-   Ar² is selected from substituted or unsubstituted C₁₈ to C₄₀ arylene    and substituted or unsubstituted C₁₀ to C₄₀ heteroarylene;

-   R⁴ is selected from H, C₁ to C₁₂ alkyl, substituted or unsubstituted    C₆ to C₂₀ aryl and substituted or unsubstituted C₅ to C₂₀    heteroaryl.

According to another aspect there is provided an organic light emittingdiode (OLED), wherein in Formula Ia the substituent X is selected fromO.

According to another aspect the polar organic aromatic phosphinecompound according to general Formula Ia, wherein o can be 1 or 2:

-   -   o=2, the polar organic aromatic phosphine compound is a compound        having the Formula Ib:

-   -   o=1 the polar organic aromatic phosphine compound is a compound        having the Formula Ic, Id, Ie or If:

According to another aspect the polar organic aromatic phosphinecompound can be selected from Formula Ib:

wherein:X is selected from O, S, Se;

-   R¹ and R² are independently selected from C₁ to C₁₂ alkyl,    substituted or unsubstituted C₆ to C₂₀ aryl and substituted or    unsubstituted C₅ to C₂₀ heteroaryl; or R¹ and R² are bridged with an    alkene-di-yl group forming with the P atom a substituted or    unsubstituted five, six or seven member ring; and-   Ar¹ is selected from substituted or unsubstituted C₆ to C₂₀ arylene    and substituted or unsubstituted C₅ to C₂₀ heteroarylene;-   Ar² is selected from substituted or unsubstituted C₁₈ to C₄₀ arylene    and substituted or unsubstituted C₁₀ to C₄₀ heteroarylene;-   R⁴ is selected from H, C₁ to C₁₂ alkyl, substituted or unsubstituted    C₆ to C₂₀ aryl and substituted or unsubstituted C₅ to C₂₀    heteroaryl.

According to another aspect the polar organic aromatic phosphinecompound can be selected from the group comprising a polar organicaromatic phosphine compound of Formula Ic and/or Id:

wherein:

-   X is selected from O, S, Se;-   R¹ and R² are independently selected from C₁ to C₁₂ alkyl,    substituted or unsubstituted C₆ to C₂₀ aryl and substituted or    unsubstituted C₅ to C₂₀ heteroaryl; or R¹ and R² are bridged with an    alkene-di-yl group forming with the P atom a substituted or    unsubstituted five, six or seven member ring; and-   Ar¹ is selected from substituted or unsubstituted C₆ to C₂₀ arylene    and substituted or unsubstituted C₅ to C₂₀ heteroarylene;-   R⁴ is selected from H, C₁ to C₁₂ alkyl, substituted or unsubstituted    C₆ to C₂₀ aryl and substituted or unsubstituted C₅ to C₂₀    heteroaryl.

According to another aspect the polar organic aromatic phosphinecompound can be selected from the group comprising a polar organicaromatic phosphine compound of Formula Id or If:

wherein:X is selected from O, S, Se;

-   R¹ and R² are independently selected from C₁ to C₁₂ alkyl,    substituted or unsubstituted C₆ to C₂₀ aryl and substituted or    unsubstituted C₅ to C₂₀ heteroaryl; or R¹ and R² are bridged with an    alkene-di-yl group forming with the P atom a substituted or    unsubstituted five, six or seven member ring; and-   Ar¹ is selected from substituted or unsubstituted C₆ to C₂₀ arylene    and substituted or unsubstituted C₅ to C₂₀ heteroarylene;-   Ar² is selected from substituted or unsubstituted C₁₈ to C₄₀ arylene    and substituted or unsubstituted C₁₀ to C₄₀ heteroarylene;-   R⁴ is selected from H, C₁ to C₁₂ alkyl, substituted or unsubstituted    C₆ to C₂₀ aryl and substituted or unsubstituted C₅ to C₂₀    heteroaryl.

According to another aspect Ar¹ and Ar² of the polar organic aromaticphosphine compound, preferably organic aromatic phosphine oxidecompound, according to Formula Ia may be defined, wherein

-   -   Ar¹ is selected from substituted C₆ to C₂₀ arylene, and/or        substituted C₅ to C₂₀ heteroarylene, wherein the C₆ to C₂₀        arylene, and/or C₅ to C₂₀ heteroarylene is substituted with at        least one C₁ to C₁₂ alkyl and/or at least one C₁ to C₁₂        heteroalkyl group; and        -   Ar² is selected from substituted C₁₈ to C₄₀ arylene and/or            substituted C₁₀ to C₄₀ heteroarylene, wherein the C₁₈ to C₄₀            arylene and/or C₁₀ to C₄₀ heteroarylene is substituted with            at least one C₁ to C₁₂ alkyl and/or at least one C₁ to C₁₂            heteroalkyl group; or        -   preferably Ar¹=substituted C₆ to C₂₀ arylene and/or            substituted C₅ to C₂₀ heteroarylene, wherein the C₆ to C₂₀            arylene and/or C₅ to C₂₀ heteroarylene is substituted with            at least one C₁ to C₆ alkyl and/or C₁ to C₆ heteroalkyl            group; and        -   Ar²=substituted C₆ to C₄₀ arylene and/or substituted C₁₀ to            C₄₀ heteroarylene, wherein the C₁₈ to C₄₀ arylene and/or C₁₀            to C₄₀ heteroarylene is substituted with at least one C₁ to            C₆ alkyl and/or C₁ to C₆ heteroalkyl group; or    -   more preferred Ar¹=substituted C₆ to C₂₀ arylene and/or        substituted C₅ to C₂₀ heteroarylene, wherein the C₆ to C₂₀        arylene and/or C₅ to C₂₀ heteroarylene is substituted with at        least one C₁ to C₄ alkyl and/or C₁ to C₄ heteroalkyl group; and    -   Ar²=substituted C₁₈ to C₄₀ arylene and/or substituted C₁₀ to C₄₀        heteroarylene, wherein the C₁₈ to C₄₀ arylene and/or C₁₀ to C₄₀        heteroarylene is substituted with at least one C₁ to C₄ alkyl        and/or C₁ to C₄ heteroalkyl group.

According to another aspect R¹ to R⁴ of the polar organic aromaticphosphine compound, preferably organic aromatic phosphine oxidecompound, according to Formula Ia may be defined, wherein

-   R¹ and R² are independently selected from substituted C₆ to C₂₀    aryl, and/or substituted C₅ to C₂₀ heteroaryl, wherein the C₆ to C₂₀    aryl, and/or C₅ to C₂₀ heteroaryl is substituted with at least one    C₁ to C₁₂ alkyl and/or at least one C₁ to C₁₂ heteroalkyl group, and    preferably R¹ and R² is selected the same; and/or-   R³ is independently selected from substituted C₆ to C₂₀ arylene,    and/or substituted C₅ to C₂₀ heteroarylene, wherein the C₆ to C₂₀    arylene, and/or C₅ to C₂₀ heteroarylene is substituted with at least    one C₆ to C₂₀ alkyl and/or at least one C₁ to C₁₂ heteroalkyl group,    and/or-   R⁴ is independently selected from substituted C₆ to C₂₀ aryl, and/or    substituted C₅ to C₂₀ heteroaryl, wherein the C₆ to C₂₀ aryl, and/or    C₅ to C₂₀ heteroaryl is substituted with at least one C₁ to C₁₂    alkyl and/or at least one C₁ to C₁₂ heteroalkyl group.

According to another aspect R¹ to R⁴, X, n, m, Ar¹ and Ar² of the polarorganic aromatic phosphine compound, preferably organic aromaticphosphine oxide compound, according to Formula Ia may be defined,wherein

-   R¹ and R² is independently selected from C₁ to C₄ alkyl,    unsubstituted or substituted C₆ to C₁₀ aryl or unsubstituted or    substituted C₅ to C₁₀ heteroaryl; preferably R¹ and R² is    independently selected from methyl, phenyl, naphthyl, phenanthryl,    pyrenyl or pyridyl; further preferred R¹ and R² are independently    selected from methyl, phenyl and pyridyl; and more preferred,    -   R¹ and R² is selected the same; and/or    -   X is O or S, and preferably 0; and/or-   R³ is selected from C₁ to C₆ alkane-di-yl, unsubstituted or    substituted C₆ to C₁₀ arylene or unsubstituted or substituted C₅ to    C₁₀ heteroarylene, and preferably selected from C₁ to C₄    alkane-di-yl; and/or-   R⁴ is selected from H, phenyl, biphenyl, terphenyl, fluorenyl,    naphthyl, anthranyl, phenanthryl, pyrenyl, carbazoyl,    dibenzofuranyl, dinapthofuranyl, preferably H, phenyl, biphenyl or    naphthyl, and more preferred H; and/or-   n is 0 or 1, and preferably n is 1, preferably for n=2 than Ar^(i)    is phenyl, and more preferred for n=1, R¹ and R² are phenyl and R⁴    is H;-   m is 1 or 2 if n is 0 or 1, and m is 2 if n is 2; and/or-   Ar¹ is preferably selected from phenylene, biphenylene,    terphenylene, naphthylene, fluorenylene, pyridylene, quinolinylene,    and pyrimidinylene; and/or-   Ar² is selected from fluorenylene, anthranylene, pyrenylene,    phenanthrylene, carbazoylene, benzo[c]acridinylene,    dibenzo[c,h]acridinylene, dibenzo[a,j] acridinylene.

According to another aspect R¹ to R⁴, Ar¹ and Ar² of the polar organicaromatic phosphine compound, preferably organic aromatic phosphine oxidecompound, according to Formula Ia may be defined, wherein R¹, R², R³,R⁴, Ar¹ and/or Ar² are unsubstituted.

According to another aspect R¹ and R² of the polar organic aromaticphosphine compound, preferably organic aromatic phosphine oxidecompound, according to Formula Ia may be independently selected from C₁to C₁₂ alkyl, preferably C₁ to C₈, even more preferred C₁ to C₆, and maybe most preferred C₁ to C₄.

According to another aspect R⁴ of the polar organic aromatic phosphinecompound, preferably organic aromatic phosphine oxide compound,according to Formula Ia may be selected from C₁ to C₁₂ alkyl, preferablyC₁ to C₈, even more preferred C₁ to C₆, most preferred C₁ to C₄.

According to another aspect Ar² of the polar organic aromatic phosphinecompound, preferably organic aromatic phosphine oxide compound,according to Formula Ia may be defined, wherein Ar² is selected from asubstituent according to Formula IVa to IVh:

According to another aspect, the polar organic aromatic phosphinecompound of Formula (Ia) is defined, wherein A¹ is selected from Formula(II).

Preferably, R³ is selected from C₁ to C₆ alkane-di-yl, unsubstituted orsubstituted C₆ to C₁₀ arylene or unsubstituted or substituted C₅ to C₁₀heteroarylene, and preferably selected from C₁ to C₄ alkane-di-yl.

Preferred examples are shown in Table 3 below. These compounds have beenfound to have particularly beneficial effect on operating voltage,external quantum efficiency (EQE) and/or lifetime.

TABLE 3 Organic aromatic phosphine oxide compounds of Formula (Ia)wherein A¹ is Formula (II) Name Structure ethane-1,2-diylbis(diphenylphosphine oxide)

butane-1,4- diylbis(diphenylphosphine oxide)

ethane-1,2- diylbis(di(naphthalen-2- yl)phosphine oxide)

(9-phenyl-9H-carbazole- 2,7- diyl)bis(diphenylphosphine oxide)

[1,1′:4′,1″-terphenyl]-3,5- diylbis(diphenylphosphine oxide)

[1,1′-binaphthalene]-2,2′- diylbis(diphenylphosphine oxide)

According to another aspect, the polar organic aromatic phosphinecompound of Formula (Ia), wherein A¹ can be selected from Formula (III).Preferably, o is 1 and n is 0 or 1 and m is 1 or 2. The molecular weightof these compounds is in a range which is particularly suitable forvacuum deposition and particularly low operating voltages, highefficiencies and/or long lifetime are achieved. Particularly preferredexamples are shown in Table 4 below.

TABLE 4 Organic aromatic phosphine oxide compounds of Formula (Ia)wherein A1 is Formula (III) Name Structure (4-(anthracen-9-yl)phenyl)diphenylphosphine oxide

(3-(phenanthren-9- yl)phenyl)diphenylphosphine oxide

(4-(phenanthren-9- yl)phenyl)diphenylphosphine oxide

(3-(phenanthren-9- yl)phenyl)diphenylphosphine oxide

diphenyl(3-(pyren-1- yl)phenyl)phosphine oxide

diphenyl(4′-(pyren-1-yl)-[1,1′- biphenyl]-3-yl)phosphine oxide

diphenyl(3′-(pyren-1-yl)-[1,1′- biphenyl]-3-yl)phosphine oxide

diphenyl(3′-(pyren-1-yl)-[1,1′- biphenyl]-4-yl)phosphine oxide

diphenyl(3″-(pyren-1-yl)- [1,1′:4′,1″-terphenyl]-3- yl)phosphine oxide

(3-(dinaphtho[2,1-b:1′,2′- d]furan-6- yl)phenyl)diphenylphosphine oxide

diphenyl(4-(9-phenyl-9H- carbazol-3- yl)phenyl)phosphine oxide

(3′,5′-di(pyren-1-yl)-[1,1′- biphenyl]-3- yl)diphenylphosphine oxide

In another preferred embodiment, o is 2 and n is 0 or 1 and m is 1. Thecrystallinity of these compounds is reduced and low operating voltagesare achieved. Particularly preferred examples are shown in Table 4above.

Polar organic aromatic phosphine compound that can be suitable used forthe polar organic aromatic phosphine compound comprising electrontransport layer/s, may have the Formula (Ia), wherein A¹ is phenyl andR¹ and R² are bridged with an alkene-di-yl group forming with the P atoma five and seven membered ring. These polar organic aromatic phosphinecompounds may provide high glass transition temperature Tg andparticularly low operating voltage, high external quantum efficiency(EQE) and/or long lifetime. Particularly preferred are the polar organicaromatic phosphine compounds that are shown in Table 5.

TABLE 5 Phosphine oxide compounds of Formula (Ia), wherein R¹ and R² arebridged with an alkene-di-yl group forming with the P atom a five andseven membered ring Name Structure 3-Phenyl-3H- benzo[b]dinaphtho[2,1-d:1′,2′- f]phosphepine-3-oxide

1,2,3,4,5- pentaphenylphosphole 1-oxide

5- phenylbenzo[b]phosphindole 5-oxide

According to another aspect the organic aromatic phosphine oxidecompound according to the invention may be selected from a compoundaccording to Formula A1 to A27:

It is further preferred that the organic aromatic phosphine oxidecompounds are substituted with a C₆-C₄₀ aryl, C₅-C₄₀ heteroaryl and/orC₁-C₁₂ alkyl groups, preferably(3-(dibenzo[c,h]acridin-7-yl)phenyl)diphenylphosphine oxide,3-phenyl-3H-benzo[b]di-naphtho[2,1-d:1′,2′-f]phosphepine-3-oxide,phenyldi(pyren-1-yl)phosphine oxide,bis(4-(anthracen-9-yl)phenyl)(phenyl)phosphine oxide,(3-(9,10-di(naphthalen-2-yl)anthracen-2-yl)phenyl)diphenylphosphineoxide, phenyldi(pyren-1-yl)phosphine oxide,diphenyl(5-(pyren-1-yl)pyridin-2-yl)phosphine oxide,diphenyl(4′-(pyren-1-yl)-[1,1′-biphenyl]-3-yl)phosphine oxide,diphenyl(4′-(pyren-1-yl)-[1,1′-biphenyl]-3-yl)phosphine oxide,(3′-(dibenzo[c,h]acridin-7-yl)-[1,1′-biphenyl]-4-yl)diphenylphosphineoxide and/or phenyl bis(3-(pyren-1-yl)phenyl)phosphine oxide.

According to another aspect, the polar organic aromatic phosphinecompound is not an emitter dopant and does not emit visible light atoperation of the OLED.

According to another aspect, the polar organic aromatic phosphinecompound is not an emitter matrix compound.

According to another embodiment of the electron transport layer stack:

-   -   the first organic aromatic matrix compounds with a dipole        moment≥0 Debye and ≤2.5 Debye can be selected from the compounds        below:

-   -   the polar organic aromatic phosphine compound can be:

Non-Emitter Dopant

According to various embodiments of the OLED of the present invention,the first electron transport layer (161) is free of a non-emitter dopantand the second electron transport layer (162) comprises a non-emitterdopant, wherein the non-emitter dopant is a metal compound, preferablythe metal compound is selected from the group comprising a metal halide,a metal organic complex and/or a zero-valent metal.

According to various embodiments of the OLED of the present invention,the metal halide may be selected from the group comprising halidewherein the metal is selected from the group comprising Li, Na, K, Cs,Mg, Ca, Ba; and the halide is selected from the group comprising F, Cl,Br and J; and preferably a lithium halide.

The lithium halide may be selected from the group comprising a LiF,LiCI, LiBr or LiJ, and preferably LiF.

According to various embodiments of the OLED of the present invention,the metal organic complex may be selected from the group of metalquinolate, a metal borate, a metal phenolate and/or a metal Schiff base.

Preferably the metal organic complex may be an alkali organic complex,preferably a lithium organic complex.

Preferably the lithium organic complex can be selected from the group ofa lithium quinolate, a lithium borate, a lithium phenolate and/or alithium Schiff base, preferably of a lithium quinolate complex has theformula I, II or III:

wherein

-   -   A₁ to A₆ are same or independently selected from CH, CR, N, O,    -   —R is same or independently selected from hydrogen, halogen,        alkyl or aryl or heteroaryl with 1 to 20 carbon atoms, and more        preferred of a lithium 8-hydroxyquinolate.

According to various embodiments of the organic electroluminescentdevice of the present invention the organic ligand of the lithiumorganic complex can be a borate based organic ligand. Preferably, thelithium organic complex is a compound of formula (VII)

wherein M is an alkali metal ion, each of A¹-A⁴ is independentlyselected from substituted or unsubstituted C₆-C₂₀ aryl or substituted orunsubstituted C₂-C₂₀ heteroaryl.Preferably, the alkali organic complex is a complex of formula (VIII)

wherein each of A¹-A⁴ is independently selected from substituted orunsubstituted C₆-C₂₀ aryl or substituted or unsubstituted C₂-C₂₀heteroaryl.

Preferably the lithium organic complex is a lithiumtetra(1H-pyrazol-1-yl)borate. Borate based organic ligands that can besuitable used are disclosed in WO 2013079676 A1.

According to various embodiments of the organic electroluminescentdevice of the present invention the organic ligand of the lithiumorganic complex can be a phenolate ligand. According to variousembodiments of the organic electroluminescent device of the presentinvention the organic ligand of the lithium organic complex can be aphosphoryl phenolate ligand.

Preferably the lithium organic complex is a phosphoryl phenolatecompound of formula (IX):

wherein A⁵ is a C₆-C₂₀ arylene and each of A⁶-A⁷ is independentlyselected from a C₆-C₂₀ aryl, wherein A⁵, A⁶ and A⁷ may be unsubstitutedor substituted with groups comprising C and H or with a further LiOgroup, provided that the given C count in an aryl or arylene groupincludes also all substituents present on the said group. Preferably thelithium organic complex is a lithium 2-(diphenylphosphoryl)phenolate.Phenolate ligands that can be suitable used are disclosed in WO2013079678 A1.

Further, phenolate ligands can be selected from the group comprisingpyridinolate, preferably 2-(diphenylphosphoryl)pyridin-3-olate. Pyridinephenolate ligands that can be suitable used are disclosed in JP2008195623.

In addition, phenolate ligands can be selected from the group comprisingimidazole phenolates, preferably2-(1-phenyl-1H-benzo[d]imidazol-2-yl)phenolate. Imidazol phenolateligands that can be suitable used are disclosed in JP 2001291593.

Also, phenolate ligands can be selected from the group comprising oxazolphenolates, preferably 2-(benzo[d]oxazol-2-yl)phenolate. Oxazolphenolate ligands that can be suitable used are disclosed in US20030165711.

According to various embodiments of the organic electroluminescentdevice of the present invention the organic ligand of the lithiumorganic complex can be a phosphoryl heteroaryloate ligand.

Preferably the lithium organic complex is a phosphoryl heteroaryloatecompound of formula (X):

wherein A⁸, A⁹ and A¹⁰ are independently selected from C₁-C₃₀-alkyl,C₃-C₃₀-cycloalkyl, C₂-C₃₀-heteroalkyl, C₆-C₃₀-aryl, C₂-C₃₀-heteroaryl,C₁-C₃₀-alkoxy, C₃-C₃₀-cycloalkyloxy, C₆-C₃₀-aryloxy, and from structuralunit having general formula E-Z—,wherein Z is a spacer unit containing trivalent nitrogen atom bearing alone electron pair, wherein the spacer unit has a structure which allowsformation of a 5-, 6- or 7-membered chelate ring with the metal cation,wherein the chelate ring comprises the oxygen atom of the phosphineoxide group and trivalent nitrogen atom of the spacer unit coordinatedto the metal cation and E is an electron transporting unit comprising aconjugated system of at least 10 delocalized electrons, andat least one group selected from A⁸, A⁹ and A¹⁰ has the general formulaE-Z—.

Preferably the lithium organic complex is a lithium2-(diphenylphosphoryl)pyridin-3-olate. Heteroarylolate ligands that canbe suitable used are disclosed in EP 2724388 and incorporated byreference.

According to various embodiments of the organic electroluminescentdevice of the present invention the organic ligand of the alkali organiccomplex can be selected from a borate ligand and a phosphoryl phenolateligand and a heteroarylolate ligand. Preferably, the organic ligand ofthe alkali organic complex is selected from a borate ligand and aphosphoryl phenolate ligand.

More preferably the lithium organic complex can be selected from thegroup comprising a lithium quinolate, a lithium borate, a lithiumphenolate, a lithium pyridinolate or a lithium Schiff base; preferably

-   -   the lithium organic complex, is selected from the group        comprising a lithium quinolate, a lithium borate, a lithium        phenolate, a lithium pyridinolate or a lithium Schiff base;    -   preferably the lithium quinolate has the formula XI, XII or        XIII:

wherein

A₁ to A₆ are same or independently selected from CH, CR, N, O;

R is same or independently selected from hydrogen, halogen, alkyl oraryl or heteroaryl with 1 to 20 carbon atoms; and more preferred A₁ toA₆ are CH;

-   -   preferably the lithium borate is a lithium        tetra(1H-pyrazol-1-yl)borate;    -   preferably the lithium phenolate is a lithium        2-(pyridin-2-yl)phenolate, a lithium        2-(diphenylphosphoryl)phenolate, a lithium imidazol phenolates,        or a lithium 2-(pyridin-2-yl)phenolate and more preferred a        lithium 2-(1-phenyl-1H-benzo[d]imidazol-2-yl)phenolate, or a        lithium 2-(benzo[d]oxazol-2-yl)phenolate;    -   preferably the lithium pyridinolate is a lithium        2-(diphenylphosphoryl)pyridin-3-olate,    -   preferably the lithium Schiff base has the structure 100, 101,        102 or 103:

Quinolates that can be suitable used are disclosed in WO 2013079217 A1.

According to various embodiments of the organic electroluminescentdevice of the present invention the organic ligand of the lithiumorganic complex can be a phenolate ligand, Preferably the lithiumorganic complex is a lithium 2-(diphenylphosphoryl)phenolate. Phenolateligands that can be suitable used are disclosed in WO 2013079678 A1.

Further, phenolate ligands can be selected from the group comprisingpyridinolate, preferably 2-(diphenylphosphoryl)pyridin-3-olate. Pyridinephenolate ligands that can be suitable used are disclosed in JP2008195623.

In addition, phenolate ligands can be selected from the group comprisingimidazol phenolates, preferably2-(1-phenyl-1H-benzo[d]imidazol-2-yl)phenolate. Imidazole phenolateligands that can be suitable used are disclosed in JP 2001291593.

Also, phenolate ligands can be selected from the group comprising oxazolphenolates, preferably 2-(benzo[d]oxazol-2-yl)phenolate. Oxazolphenolate ligands that can be suitable used are disclosed in US20030165711.

Lithium Schiff base organic complexes can be use. Lithium Schiff baseorganic complexes that can be suitable used having the structure 100,101, 102 or 103:

Suitable organic ligands to form a lithium organic complex that can beused for the electron injection layer are disclosed in US 2014/0048792and Kathirgamanathan, Poopathy; Arkley, Vincent; Surendrakumar,Sivagnanasundram; Chan, Yun F.; Ravichandran, Seenivasagam;Ganeshamurugan, Subramaniam; Kumaraverl, Muttulingam; Antipan-Lara,Juan; Paramaswara, Gnanamolly; Reddy, Vanga R., Digest of TechnicalPapers—Society for Information Display International Symposium (2010),41(Bk. 1), 465-468.

Extraordinary preferred lithium organic complexes which may be used inthe present invention are summarized in the following Table 6.

TABLE 6 Lithium organic complex that can be suitable used Compound NameStructure Reference LiQ lithium 8-hydroxyquinolate

WO 2013079217 A1 Li-1 lithium tetra(1H-pyrazol-1- yl)borate

WO 2013079676 A1 Li-2 lithium 2-(diphenyl- phosphoryl)phenolate

WO 2013079678A1 Li-3 lithium 2-(pyridin-2- yl)phenolate

JP2 008195623 Li-4 lithium 2-(1-phenyl-1H- benzo[d]imidazol-2-yl)phenolate

JP 2001291593 Li-5 lithium 2-(benzo[d]oxazol-2- yl)phenolate

U.S. 20030165711 Li-6 lithium 2-(diphenyl- phosphoryl)pyridin-3-olate

EP 2724388

According to various embodiments of the OLED of the present invention,the zero-valent metal, is selected from the group comprising alkalimetal, alkaline earth metal, rare earth metal and/or a group 3transition metal, preferably the zero-valent metal is selected from thegroup comprising Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, Yb, Sm, Eu, Nd, Tb,Gd, Ce, La, Sc and Y, more preferred the zero-valent metal is selectedfrom the group comprising Li, Na, Mg, Ca, Ba, Yb, and further morepreferred the zero-valent metal is selected from the group comprisingLi, Mg, Ba, Yb.

According to another aspect, the second electron transport layercomprises a non-emitter dopant, wherein the non-emitter dopant is ametal organic complex of a lithium quinolate, a lithium borate, alithium phenolate and/or a lithium Schiff base, preferably of a lithiumquinolate complex having the formula I, II or III.

According to another aspect, the second electron transport layercomprises a non-emitter dopant, wherein the non-emitter dopant is ametal organic complex of a borate based organic ligand, preferably, thelithium organic complex is a compound of formula (VII)

wherein M is an alkali metal ion, each of A¹-A⁴ is independentlyselected from substituted or unsubstituted C₆-C₂₀ aryl or substituted orunsubstituted C₂-C₂₀ heteroaryl; or an alkali organic complex of formula(VIII)

wherein each of A¹-A⁴ is independently selected from substituted orunsubstituted C₆-C₂₀ aryl or substituted or unsubstituted C₂-C₂₀heteroaryl; or an Li organic complex of formula (VIII)

wherein each of A¹-A⁴ is independently selected from substituted orunsubstituted C₆-C₂₀ aryl or substituted or unsubstituted C₂-C₂₀heteroaryl.

According to another aspect, the second electron transport layercomprises a non-emitter dopant, wherein the non-emitter dopant is ametal compound, preferably the metal compound is selected from the groupcomprising a metal halide, a metal organic complex and/or a zero-valentmetal; and more preferred the metal organic complex has the formula VII:

in addition preferred the metal organic complex is a lithium borate, andmost preferred lithium tetra(1H-pyrazol-1-yl)borate.

According to another aspect, the first electron transport layer is freeof a non-emitter dopant and the second electron transport layercomprises a non-emitter dopant, wherein the non-emitter dopant is ametal compound, preferably the metal compound is selected from the groupcomprising a metal halide, a metal organic complex and/or a zero-valentmetal; and more preferred the metal organic complex has the formula VII:

wherein M is an alkali metal ion, each of A¹-A⁴ is independentlyselected from substituted or unsubstituted C₆-C₂₀ aryl or substituted orunsubstituted C₂-C₂₀ heteroaryl, even more preferred M is lithium ion,and most preferred lithium tetra(1H-pyrazol-1-yl)borate.

Substrate

The substrate may be any substrate that is commonly used inmanufacturing of organic light-emitting diodes. If light is emittedthrough the substrate, the substrate may be a transparent material, forexample a glass substrate or a transparent plastic substrate, havingexcellent mechanical strength, thermal stability, transparency, surfacesmoothness, ease of handling, and waterproofness. If light is emittedthrough the top surface, the substrate may be a transparent ornon-transparent material, for example a glass substrate, a plasticsubstrate, a metal substrate or a silicon substrate.

Anode Electrode

The anode electrode may be formed by depositing or sputtering a compoundthat is used to form the anode electrode. The compound used to form theanode electrode may be a high work-function compound, so as tofacilitate hole injection. The anode material may also be selected froma low work function material (i.e. Aluminum). The anode electrode may bea transparent or reflective electrode. Transparent conductive compounds,such as indium tin oxide (ITO), indium zinc oxide (IZO), tin-dioxide(SnO₂), and zinc oxide (ZnO), may be used to form the anode electrode120. The anode electrode 120 may also be formed using magnesium (Mg),aluminum (Al), aluminum-lithium (Al—Li), calcium (Ca), magnesium-indium(Mg—In), magnesium-silver (Mg—Ag), silver (Ag), gold (Au), or the like.

The anode electrode may be formed from a high conductivity metal, forexample copper (Cu) or silver (Ag).

HIL

A hole injection layer (HIL), comprising a first and/or second holeinjection layer, that can be suitable used for the OLED of the presentinvention are described in US2002158242 AA, EP1596445A1 and EP1988587A1.

The first HIL may be formed on the anode electrode by vacuum deposition,spin coating, printing, casting, slot-die coating, Langmuir-Blodgett(LB) deposition, or the like.

The second HIL may be formed on the n-type charge generation layer byvacuum deposition, spin coating, slot-die coating, printing, casting,Langmuir-Blodgett (LB) deposition, or the like.

When the HIL is formed using vacuum deposition, the depositionconditions may vary according to the compound that is used to form theHIL, and the desired structure and thermal properties of the HIL. Ingeneral, however, conditions for vacuum deposition may include adeposition temperature of 100° C. to 500° C., a pressure of 10⁻⁸ to 10⁻³torr (1 torr equals 133.322 Pa), and a deposition rate of 0.1 to 10nm/sec.

For example, the coating conditions may include a coating speed of about2000 rpm to about 5000 rpm, and a thermal treatment temperature of about80° C. to about 200° C. Thermal treatment removes a solvent after thecoating is performed.

HTL

A hole transport layer (HTL), comprising a first and/or second holetransport layer, that can be suitable used for the OLED of the presentinvention are described in Shirota and Kageyama, Chem. Rev. 2007, 107,953-1010.

The first hole transport layer (HTL) may be formed on the HIL by vacuumdeposition, spin coating, slot-die coating, printing, casting,Langmuir-Blodgett (LB) deposition, or the like.

The second hole transport layer (HTL) may be formed on the second holeinjection layer by vacuum deposition, spin coating, slot-die coating,printing, casting, Langmuir-Blodgett (LB) deposition, or the like.

When the HTL is formed by vacuum deposition or spin coating, theconditions for deposition and coating may be similar to those for theformation of the HIL. However, the conditions for the vacuum or solutiondeposition may vary, according to the compound that is used to form theHTL.

Electron Blocking Layer

The function of the electron blocking layer (EBL) 150 is to preventelectrons from being transferred from the emission layer to the holetransport layer and thereby confine electrons to the emission layer.Thereby, efficiency, operating voltage and/or lifetime are improved.Typically, the electron blocking layer comprises a triarylaminecompound. The triarylamine compound may have a LUMO level closer tovacuum level than the LUMO level of the hole transport layer. Theelectron blocking layer may have a HOMO level that is further away fromvacuum level compared to the HOMO level of the hole transport layer. Thethickness of the electron blocking layer is selected between 2 and 20nm.

The electron blocking layer may comprise a compound of Formula Z below

In Formula Z, CY1 and CY2 are the same as or different from each other,and each independently represent a benzene cycle or a naphthalene cycle,

Ar1 to Ar3 are the same as or different from each other, and eachindependently selected from the group consisting of hydrogen; asubstituted or unsubstituted aryl group having 6 to 30 carbon atoms; anda substituted or unsubstituted heteroaryl group having 5 to 30 carbonatoms,

Ar4 is selected from the group consisting of a substituted orunsubstituted phenyl group, a substituted or unsubstituted biphenylgroup, a substituted or unsubstituted terphenyl group, a substituted orunsubstituted triphenylene group, and a substituted or unsubstitutedheteroaryl group having 5 to 30 carbon atoms,

L is a substituted or unsubstituted arylene group having 6 to 30 carbonatoms.

If the electron blocking layer has a high triplet level, it may also bedescribed as triplet control layer.

The function of the triplet control layer is to reduce quenching oftriplets if a phosphorescent green or blue emission layer is used.Thereby, higher efficiency of light emission from a phosphorescentemission layer can be achieved. The triplet control layer is selectedfrom triarylamine compounds with a triplet level above the triplet levelof the phosphorescent emitter in the adjacent emission layer. Suitabletriplet control layer, in particular the triarylamine compounds, aredescribed in EP 2 722 908 A1, and fully incorporated by reference.

Emission Layer (EML)

The EML may be formed on the HTL by vacuum deposition, spin, coating,slot-die coating, printing, casting, LB, or the like. When the EML isformed using vacuum deposition or spin coating, the conditions fordeposition and coating may be similar to those for the formation of theHIL.

The first emission layer may be formed on the first hole transportlayer.

The second emission layer may be formed on the second hole transportlayer.

However, the conditions for deposition and coating may vary, accordingto the compound that is used to form the EML.

The emission layer (EML) may be formed of a combination of a host and adopant. Example of the host are Alq3, 4,4′-N,N′-dicarbazole-biphenyl(CBP), poly(n-vinylcarbazole) (PVK),9,10-di(naphthalene-2-yl)anthracenee (ADN),4,4′,4″-Tris(carbazol-9-yl)-triphenyl-amine (TCTA),1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBI),3-tert-butyl-9,10-di-2-naphthylanthracenee (TBADN), distyrylarylene(DSA), Bis(2-(2-hydroxyphenyl)benzothiazolate)zinc (Zn(BTZ) 2), E3below, AND, Compound 12 below, and Compound 13 below.

In a preferred embodiment, the emission layer comprises at least oneemitter dopant that emits visible light at operation of the OLED.

The dopant may be a phosphorescent or fluorescent emitter.Phosphorescent emitters and emitters which emit light via a thermallyactivated delayed fluorescence (TADF) mechanism are preferred due totheir higher efficiency. The emitter may be a small molecule or apolymer. Examples of a red dopant are PtOEP, Ir(piq)₃, and Btp2lr(acac), but are not limited thereto. These compounds arephosphorescent emitters, however, fluorescent red dopants could also beused.

Examples of a phosphorescent green dopant are Ir(ppy)₃(ppy=phenylpyridine), Ir(ppy)₂(acac), Ir(mpyp)₃ are shown below.Compound 14 is an example of a fluorescent green emitter and thestructure is shown below.

Examples of a phosphorescent blue dopant are F₂Irpic, (F₂ppy)₂Ir(tmd)and Ir(dfppz) 3, ter-fluorene, the structures are shown below.4.4′-bis(4-diphenyl amiostyryl)biphenyl (DPAVBi),2,5,8,11-tetra-tert-butyl perylene (TBPe), and Compound 15 below areexamples of fluorescent blue dopants.

The amount of the dopant may be in the range of about 0.01 to about 50parts by weight, based on 100 parts by weight of the host.Alternatively, the emission layer may comprise or consist of alight-emitting polymer. The EML may have a thickness of about 10 nm toabout 100 nm, for example, about 20 nm to about 60 nm. When thethickness of the EML is within this range, the EML may have excellentlight emission, without a substantial increase in driving voltage.

In a preferred embodiment, the emission layer comprising or consistingof the light-emitting polymer is in direct contact with the electrontransport layer stack.

Hole Blocking Layer (HBL)

When the EML comprises a phosphorescent dopant, a hole blocking layer(HBL) may be formed on the EML, by using vacuum deposition, spincoating, slot-die coating, printing, casting, LB deposition, or thelike, in order to prevent the diffusion of triplet excitons or holesinto the ETL.

Hole blocking layer that can be suitable used for the OLED of thepresent invention are described in US2015207093A and US2015060794A, andfully incorporated by reference.

When the HBL is formed using vacuum deposition or spin coating, theconditions for deposition and coating may be similar to those for theformation of the HIL. However, the conditions for deposition and coatingmay vary, according to the compound that is used to form the HBL. Anycompound that is commonly used to form a HBL may be used. Examples ofcompounds for forming the HBL include an oxadiazole derivative, atriazole derivative, a triazine derivative, an acridine derivative, anda phenanthroline derivative.

If the hole blocking layer has a high triplet level, it may also bedescribed as triplet control layer. The function of the triplet controllayer is to reduce quenching of triplets if a phosphorescent green orblue emission layer is used. Thereby, higher efficiency of lightemission from a phosphorescent emission layer can be achieved. Thetriplet control layer is selected from a heteroaryl compound with atriplet level above the triplet level of the phosphorescent emitter inthe adjacent emission layer.

The first hole blocking layer may be formed on the first emission layer.

The second hole blocking layer may be formed on the second emissionlayer.

The HBL may have a thickness of about 5 nm to about 100 nm, for example,about 10 nm to about 30 nm. When the thickness of the HBL is within thisrange, the HBL may have excellent hole-blocking properties, without asubstantial increase in driving voltage.

Charge Generation Layer

Charge generation layers (CGL) that can be suitable used for the OLED ofthe present invention are described in US 2012098012 A.

The charge generation layer is generally composed of a double layer. Thecharge generation layer can be a pn junction charge generation layerjoining n-type charge generation layer and p-type charge generationlayer. The pn junction charge generation layer generates charges orseparates them into holes and electrons; and injects the charges intothe individual light emission layer. In other words, the n-type chargegeneration layer provides electrons for the first light emission layeradjacent to the anode electrode while the p-type charge generation layerprovides holes to the second light emission layer adjacent to thecathode electrode, by which luminous efficiency of an organic lightemitting device incorporating multiple light emission layers can befurther improved and at the same time, driving voltage can be lowered.

The p-type charge generation layer can be composed of metal or organicmaterial doped with p-type dopant. Here, the metal can be one or analloy consisting of two or more selected from a group consisting of Al,Cu, Fe, Pb, Zn, Au, Pt, W, In, Mo, Ni, and Ti. Also, p-type dopant andhost used for organic material doped with the p-type can employconventional materials. For example, the p-type dopant can be oneselected from a group consisting oftetrafluore-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ), derivative oftetracyanoquinodimethane, radialene derivative, iodine, FeCl3, FeF3, andSbC15. Also, the host can be one selected from a group consisting ofN,N′-di(naphthalen-1-yl)-N,N-diphenyl-benzidine (NPB),N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1-biphenyl-4,4′-diamine (TPD)and N,N′,N′-tetranaphthyl-benzidine (TNB).

The n-type charge generation layer can be composed of metal or organicmaterial doped with n-type. The metal can be one selected from a groupconsisting of Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, La, Ce, Sm, Eu, Tb, Dy,and Yb. Also, n-type dopant and host used for organic material dopedwith the n-type can employ conventional materials. For example, then-type dopant can be alkali metal, alkali metal compound, alkali earthmetal, or alkali earth metal compound. More specifically, the n-typedopant can be one selected from a group consisting of Cs, K, Rb, Mg, Na,Ca, Sr, Eu and Yb. The host material can be one selected from a groupconsisting of tris(8-hydroxyquinoline)aluminum, triazine,hydroxyquinoline derivative, benzazole derivative, and silolederivative.

In another preferred embodiment, the n-type charge generation layer isarranged adjacent to the electron transport layer. The n-type chargegeneration layer according to one embodiment may include compounds ofthe following Chemical Formula 16.

each of A¹ to A⁶ may be hydrogen, a halogen atom, nitrile (—CN), nitro(—NO₂), sulfonyl (—SO₂R), sulfoxide (—SOR), sulfonamide (—SO₂NR),sulfonate (—SO₃R), trifluoromethyl (—CF₃), ester (—COOR), amide (—CONHRor —CONRR′), substituted or unsubstituted straight-chain orbranched-chain C₁-C₁₂ alkoxy, substituted or unsubstitutedstraight-chain or branched-chain C₁-C₁₂ alkyl, substituted orunsubstituted straight-chain or branched chain C₂-C₁₂ alkenyl, asubstituted or unsubstituted aromatic or non-aromatic heteroring,substituted or unsubstituted aryl, substituted or unsubstituted mono- ordi-arylamine, substituted or unsubstituted alkylamine, or the like.

Herein, each of the above R and R′ may be substituted or unsubstitutedC₁-C₆₀ alkyl, substituted or unsubstituted aryl, or a substituted orunsubstituted 5- to 7-membered heteroring, or the like.

Particularly preferred is an n-type charge generation layer comprising acompound of Formula (17)

The p-type charge generation layer is arranged on top of the n-typecharge generation layer. As the materials for the p-type chargegeneration layer, aryl amine-based compounds may be used. One embodimentof the aryl amine-based compounds includes compounds of the followingChemical Formula 18:

Ar₁, Ar₂ and Ar₃ are each independently hydrogen or a hydrocarbon group.Herein, at least one of Ar₁, Ar₂ and Ar3 may include aromatichydrocarbon substituents, and each substituent may be the same, or theymay be composed of different substituents. When Ar₁, Ar₂ and Ar₃ are notaromatic hydrocarbons, they may be hydrogen; a straight-chain,branched-chain or cyclic aliphatic hydrocarbon; or a heterocyclic groupincluding N, O, S or Se.

In another aspect of the present invention, the organic light emittingdiode (100) further comprises an n-type CGL (185), a p-type CGL (135)and an ETL-stack (160), wherein the ETL-stack (160) comprises a firstelectron transport layer (160 a) comprising a first organic aromaticmatrix compound selected from polar organic aromatic phosphine compoundand a second electron transport layer (160 b) comprising a secondorganic matrix compound. Preferably, the polar organic aromaticphosphine compound is selected from the group of organic phosphineoxide, organic thioxophosphine compound and/or an organicselenoxophosphine compound, and the second organic matrix compound isselected from an organic compound with a dipole moment of about ≥0 Debyeand about ≤2.5 Debye. In a particularly preferred embodiment, theelectron injection layer (180) and the first electron transport layer(160) comprise the same polar organic aromatic phosphine compound.

In a preferred embodiment, the n-type CGL comprises or consists of thefirst zero-valent metal.

Electron Injection Layer (EIL)

The organic light emitting diode may comprise an electron injectionlayer. The electron injection layer may consist of at least one metalcompound.

The metal compound can be selected from the group comprising a metalhalide, a metal organic complex and/or a zero-valent metal.

Preferably, the metal compound is selected from the group comprising ametal halide, a metal organic complex and/or a zero-valent metal,preferably an alkali halide, alkali organic complex, more preferred analkali halide, alkali organic complex, most preferred are lithiumfluoride and lithium quinolate

The metal halide may be selected from the group comprising halidewherein the metal is selected from the group comprising Li, Na, K, Cs,Mg, Ca and Ba; and the halide is selected from the group comprising F,Cl, Br and J; and preferably a lithium halide.

The lithium halide may be selected from the group comprising a LiF,LiCl, LiBr or LiJ, and preferably LiF.

The metal organic complex may be selected from the group of metalquinolate, a metal borate, a metal phenolate and/or a metal Schiff base.

Preferably the metal organic complex may be a lithium organic complex.

Preferably the lithium organic complex can be selected from the group ofa lithium quinolate, a lithium borate, a lithium phenolate and/or alithium Schiff base, preferably of a lithium quinolate complex has theformula I, II or III:

wherein

-   -   A₁ to A₆ are same or independently selected from CH, CR, N, O,    -   R is same or independently selected from hydrogen, halogen,        alkyl or aryl or heteroaryl with 1 to 20 carbon atoms, and more        preferred of a lithium 8-hydroxyquinolate.

The zero-valent metal, if not defined other in the description, isselected from the group comprising alkali metal, alkaline earth metal,rare earth metal and/or a group 3 transition metal, preferably thezero-valent metal is selected from the group comprising Li, Na, K, Rb,Cs, Mg, Ca, Sr, Ba, Yb, Sm, Eu, Nd, Tb, Gd, Ce, La, Sc and Y, morepreferred the zero-valent metal is selected from the group comprisingLi, Na, Mg, Ca, Ba, Yb, and further more preferred the zero-valent metalis selected from the group comprising Li, Mg, Ba, Yb.

Preferably, the electron injection layer is free of organic matrixcompound. Therefore, the electron injection layer is not an electrontransport layer.

The electron injection layer can be sandwiched between the electrontransport layer stack and the cathode electrode layer, preferably theelectron injection layer is arranged in direct contact to the cathodeelectrode layer.

The EIL, if present, may be formed directly on the electron transportlayer stack. Deposition and coating conditions for forming the EIL aresimilar to those for formation of an hole injection layer (HIL),although the deposition and coating conditions may vary, according to amaterial that is used to form the EIL.

The thickness of the EIL may be in the range of about 1 nm to 10 nm.According to a preferred embodiment the electron injection layer may athickness of ≥1 nm and ≤10 nm, preferably ≥2 nm to ≤6 nm, preferably of≥3 nm to ≤5 nm and more preferred of ≥3 nm to ≤4 nm. When the thicknessof the EIL is within this range, the EIL according to the invention mayhave improved electron-injecting properties, especially a substantialdecrease in operating voltage and/or increase in external quantumefficiency EQE.

According to another aspect of the OLED, the second electron transportlayer, and/or the second electron transport layer and fourth electrontransport layer, comprise a polar organic aromatic phosphine compoundhaving a MW of about ≥400 to about ≤1000, and a dipole moment ofabout >2.5 Debye and about ≤10 Debye, and wherein the electron injectionlayer is free of a polar organic aromatic phosphine compound and is freeof a first organic aromatic matrix compound.

Preferably, an electron injection layer is present if the secondelectron transport layer does not contain a non-emitter dopant.

If the second electron transport layer contains a non-emitter dopant, anelectron injection layer may not be present.

Cathode Electrode

The cathode electrode is formed on the EIL. The cathode electrode is anelectron-injecting electrode. The cathode electrode may be formed of ametal, an alloy, an electrically conductive compound, or a mixturethereof. The cathode electrode may have a low work function. Forexample, the cathode may be formed of lithium (Li), magnesium (Mg),aluminum (Al), aluminum (Al)-lithium (Li), calcium (Ca), barium (Ba),ytterbium (Yb), magnesium (Mg)-indium (In), magnesium (Mg)-silver (Ag),or the like. In addition, the cathode electrode may be formed of atransparent conductive material, such as ITO or IZO.

The thickness of the cathode electrode may be in the range of about 5 nmto 1000 nm, for example, in the range of 10 nm to 100 nm. When thecathode is in the range of 5 nm to 50 nm, the electrode will transparenteven if a metal or metal alloy is used.

The cathode electrode is not an electron injection layer or electrontransport layer.

In a preferred embodiment, the cathode electrode is in direct contactwith the electron transport layer stack. Surprisingly, it was found thatvery good electron injection from the cathode electrode into theelectron transport layer stack can be achieved when the electrontransport layer which is in direct contact with the cathode comprises anon-emitter dopant. Preferably, the second electron transport layer isin direct contact with the cathode electrode.

Very low operating voltages and high external quantum efficiency EQE areachieved when the cathode electrode layer is in direct contact with anelectron injection layer. Thereby, the battery life of mobile devices isincreased. However, the cathode electrode and the electron injectionlayer, if present, differ in their components.

Light-Emitting Diode (OLED)

According to another aspect of the present invention, there is providedan organic light-emitting diode (OLED) comprising: a substrate, an anodeelectrode a hole injection layer, a hole transport layer, optional anelectron blocking layer, an emission layer, optional a hole blockinglayer, optional an electron transport layer, an electron injectionlayer, and a first cathode electrode layer, wherein the layers arearranged in that order.

According to another aspect of the present invention, there is providedan organic light-emitting diode (OLED) comprising: a substrate, an anodeelectrode a first hole injection layer, a first hole transport layer,optional first electron blocking layer, a first emission layer, optionala first hole blocking layer, optional a first electron transport layer,an n-type charge generation layer, a p-type charge generation layer, asecond hole transport layer, optional second electron blocking layer, asecond emission layer, optional a second hole blocking layer, optional asecond electron transport layer, an electron injection layer, and acathode electrode layer, wherein the layers are arranged in that order.

According to various embodiments of the OLED of the present invention,the OLED may not comprises an electron injection layer.

According to various embodiments of the OLED of the present invention,the OLED may not comprises an electron blocking layer.

According to various embodiments of the OLED of the present invention,the OLED may not comprises a hole blocking layer.

According to various embodiments of the OLED of the present invention,the OLED may not comprises a charge generation layer.

According to various embodiments of the OLED of the present invention,the OLED may not comprises a second emission layer.

Method of Manufacture

According to various embodiments of the present invention, the methodmay further include forming on a substrate an anode electrode the otherlayers of hole injection layer, hole transport layer, optional anelectron blocking layer, emission layer, optional hole blocking layer,an electron transport layer stack comprising at least a first electrontransport layer and a second electron transport layer, optional anelectron injection layer, and a cathode electrode layer, are depositedin that order; or the layers are deposited the other way around,starting with the cathode electrode layer.

According to various embodiments of the present invention, the methodmay further include that on the substrate an anode electrode isdeposited and on the anode electrode the other layers of hole injectionlayer, hole transport layer, optional an electron blocking layer,emission layer, optional hole blocking layer, an electron transportlayer stack comprising at least a first electron transport layer and asecond electron transport layer, optional an electron injection layer,and a cathode electrode layer, are deposited in that order; or thelayers are deposited the other way around, starting with the firstcathode electrode layer.

According to various embodiments of the present invention, the methodmay further include forming on a substrate an anode electrode a firsthole injection layer, a first hole transport layer, optional firstelectron blocking layer, a first emission layer, optional a first holeblocking layer, a first electron transport layer stack, an n-type chargegeneration layer, an p-type charge generation layer, a second holetransport layer, optional second electron blocking layer, a secondemission layer, optional a second hole blocking layer, optional a secondelectron transport layer stack, optional an electron injection layer, acathode electrode layer, wherein the layers are arranged in that order;or the layers are deposited the other way around, starting with thecathode electrode layer.

However, according to one aspect the layers are deposited the other wayaround, starting with the cathode electrode, and sandwiched between thecathode electrode and the anode electrode.

The anode electrode and/or the cathode electrode can be deposited on asubstrate. Preferably the anode is deposited on a substrate.

According to another aspect of the present invention, there is provideda method of manufacturing an organic light-emitting diode (OLED), themethod using:

-   -   at least one deposition source, preferably two deposition        sources and more preferred at least three deposition sources;        and/or    -   deposition via vacuum thermal evaporation; and/or    -   deposition via solution processing, preferably the processing        is-selected from spin-coating, printing, casting and/or slot-die        coating.

Electronic Device

Another aspect is directed to an electronic device comprising at leastone organic light-emitting diode (OLED). A device comprising organiclight-emitting diodes (OLED) is for example a display or a lightingpanel.

Additional aspects and/or advantages of the invention will be set forthin part in the description which follows and, in part, will be obviousfrom the description, or may be learned by practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages of the present invention willbecome apparent and more readily appreciated from the followingdescription of the exemplary embodiments, taken in conjunction with theaccompanying drawings, of which:

FIG. 1 is a schematic sectional view of an organic light-emitting diode(OLED), according to an exemplary embodiment of the present invention;

FIG. 2 is a schematic sectional view of an OLED, according to anexemplary embodiment of the present invention.

FIG. 3. is a schematic sectional view of an OLED, according to anotherexemplary embodiment of the present invention.

FIG. 4 is a schematic sectional view of an OLED, according to anotherexemplary embodiment of the present invention.

FIG. 5 is a schematic sectional view of an OLED, according to anotherexemplary embodiment of the present invention.

FIG. 6 is a schematic sectional view of an OLED, according to anotherexemplary embodiment of the present invention.

FIG. 7 is a schematic sectional view of a tandem OLED comprising acharge generation layer, according to an exemplary embodiment of thepresent invention.

DETAILED DESCRIPTION

Reference will now be made in detail to the exemplary embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to the like elementsthroughout. The exemplary embodiments are described below, in order toexplain the aspects of the present invention, by referring to thefigures.

Herein, when a first element is referred to as being formed or disposed“on” a second element, the first element can be disposed directly on thesecond element, or one or more other elements may be disposed therebetween. When a first element is referred to as being formed or disposed“directly on” a second element, no other elements are disposed therebetween.

FIG. 1 is a schematic sectional view of an organic light-emitting diode(OLED) 100, according to an exemplary embodiment of the presentinvention. The OLED 100 includes a substrate 110, an anode electrode120, a hole injection layer (HIL) 130, a hole transport layer (HTL) 140,an emission layer (EML) 150, an electron transport layer stack (ETL) 160of a first electron transport layer 161 and a second electron transportlayer 162. The first electron transport layer 161 comprises i) a firstorganic aromatic matrix compound having a MW of about ≥400 to about≤1000 and a dipole moment of about ≥0 Debye and about ≤2.5 Debye,wherein the first electron transport layer 161 is free of an polarorganic aromatic phosphine compound; and the second electron transportlayer 162 comprises two organic aromatic matrix materials, which are amixture of:

-   -   i) the first organic aromatic matrix compound; and ii) an polar        organic aromatic phosphine compound having a MW of about ≥400 to        about ≤1000, and a dipole moment of about >2.5 Debye and about        ≤10 Debye.

The polar organic aromatic phosphine compound selected from the group oforganic aromatic phosphine oxide compound or an organic aromaticthioxophosphine compound or an organic aromatic selenoxophosphinecompound. The cathode electrode layer 190 is disposed directly onto thesecond electron transport layer (ETL) 162.

FIG. 2 is a schematic sectional view of an OLED 100, according toanother exemplary embodiment of the present invention. FIG. 2 differsfrom FIG. 1 in that the OLED 100 of FIG. 2 comprises an electrontransport layer stack 160 of a first electron transport layer 161, asecond electron transport layer 162 and a third electron transport layer163. The third electron transport layer 163 may have the samecomposition as the first electron transport layer 161.

FIG. 3 is a schematic sectional view of an OLED 100, according toanother exemplary embodiment of the present invention. FIG. 3 differsfrom FIG. 1 in that the OLED 100 of FIG. 3 comprises an electrontransport layer stack 160 of a first electron transport layer 161, asecond electron transport layer 162, a third electron transport layer163, and a fourth electron transport layer 164.

FIG. 4 is a schematic sectional view of an OLED 100, according toanother exemplary embodiment of the present invention. FIG. 4 differsfrom FIG. 1 in that the OLED 100 of FIG. 4 comprises an electronblocking layer (EBL) 145 and an electron injection layer (EIL) 180.

FIG. 5 is a schematic sectional view of an OLED 100, according toanother exemplary embodiment of the present invention. FIG. 5 differsfrom FIG. 2 in that the OLED 100 of FIG. 5 comprises an electroninjection layer (EIL) 180.

FIG. 6 is a schematic sectional view of an OLED 100, according toanother exemplary embodiment of the present invention. FIG. 6 differsfrom FIG. 5 in that the OLED 100 of FIG. 6 comprises in addition anelectron blocking layer (EBL) 145.

FIG. 7 is a schematic sectional view of a tandem OLED 100 including asubstrate 110, an anode electrode 120, a first hole injection layer(HIL) 130, a first hole transport layer (HTL) 140, a first electronblocking layer (EBL) 145, a first emission layer (EML) 150, a first holeblocking layer (HBL) 155, an electron transport layer stack 160 of afirst electron transport layer (ETL) 161 and a second electron transportlayer (ETL) 162, an n-type charge generation layer (n-type CGL) 185, ap-type charge generation layer (p-type GCL) 186, a second hole transportlayer (HTL) 141, a second electron blocking layer (EBL) 146, a secondemission layer (EML) 151, a second hole blocking layer (EBL) 156, asecond electron transport layer stack (ETL) 160 of a fourth electrontransport layer (ETL) 164 and a third electron transport layer (ETL)163, an electron injection layer (EIL) 180, a first cathode electrodelayer 191 and a second cathode electrode layer 192. The second electrontransport layer 162 and the third electron transport layer 163comprising a polar organic aromatic phosphine compound selected from thegroup of organic aromatic phosphine oxide compound or an organicaromatic thioxophosphine compound or an organic aromaticselenoxophosphine compound.

In the description above the method of manufacture an OLED 100 of thepresent invention can be started with a substrate 110 onto which ananode electrode 120 is formed, on the anode electrode 120, a first holeinjection layer 130, first hole transport layer 140, an optional firstelectron blocking layer 145, a first emission layer 150, an optionalfirst hole blocking layer 155, an ETL-stack 160 comprising a firstelectron transport layer 161 and a second electron transport layer 162,an optional n-type CGL 185, optional p-type CGL 186, an optional secondhole transport layer 141, an optional second electron blocking layer146, an optional second emission layer 151, an optional second holeblocking layer 156, an optional additional ETL-stack 160 comprising afourth electron transport layer 164 and a third electron transport layer163, optional an electron injection layer 180, a first cathode electrodelayer 191 and an optional second cathode electrode layer 192 are formed,in that order or the other way around.

While not shown in FIG. 1, FIG. 2, FIG. 3, FIG. 4, FIG. 5, FIG. 6 andFIG. 7, a sealing layer may further be formed on the cathode electrodes190, in order to seal the OLED 100. In addition, various othermodifications may be applied thereto.

EXAMPLES General Procedure

Bottom Emission Devices with an Evaporated Emission Layer

For bottom emission devices—Examples 1 to 10 and comparative examples 1to 2, a 15 Ω/cm 2 glass substrate (available from Corning Co.) with 100nm ITO was cut to a size of 50 mm×50 mm×0.7 mm, ultrasonically cleanedwith isopropyl alcohol for 5 minutes and then with pure water for 5minutes, and cleaned again with UV ozone for 30 minutes, to prepare afirst electrode.

Then, 97 wt.-% ofBiphenyl-4-yl(9,9-diphenyl-9H-fluoren-2-yl)-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-amineand 3 wt.-% of2,2′,2″-(cyclopropane-1,2,3-triylidene)tris(2-(p-cyanotetrafluorophenyl)acetonitrile)was vacuum deposited on the ITO electrode, to form a HIL having athickness of 10 nm. ThenBiphenyl-4-yl(9,9-diphenyl-9H-fluoren-2-yl)-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-aminewas vacuum deposited on the HIL, to form a HTL having a thickness of 120nm. 97 wt.-% of ABH113 (Sun Fine Chemicals) as a host and 3 wt.-% ofNUBD370 (Sun Fine Chemicals) as a dopant were deposited on the HTL, toform a blue-emitting EML with a thickness of 20 nm.

Then, the first electron transport layer is formed by deposing a firstorganic aromatic matrix compound ETM1 according to examples 1 to 11 andcomparative example 1 to 29 by deposing the compound from a firstdeposition source directly on the EML. Further, the thickness d (in nm)of the ETL1 can be taken from Table 7, 8 and 9.

Then, the second electron transport layer is formed by deposing a polarorganic aromatic phosphine compound ETM2 according to example 1 to 11and comparative examples 1 to 29 directly on the first electrontransport layer. The composition and thickness of the second electrontransport layer can be taken from Table 7, 8 and 9.

If present, the electron injection layer is formed by deposing LiQ or Ybdirectly on the second electron transport layer. The composition andthickness of the second electron transport layer can be taken from Table7, 8 and 9.

The cathode electrode layer is evaporated at ultra-high vacuum of 10-7bar. Therefore, a thermal single co-evaporation of one or several metalsis performed with a rate of 0, 1 to 10 nm/s (0.01 to 1 Å/s) in order togenerate a homogeneous cathode electrode with a thickness of 5 to 1000nm. 100 nm aluminium is used as cathode layer in examples 1 to 11 andcomparative example 1 to 29.

The OLED stack is protected from ambient conditions by encapsulation ofthe device with a glass slide. Thereby, a cavity is formed, whichincludes a getter material for further protection.

Top Emission Devices

For top emission devices, the anode electrode was formed from 100 nmsilver on glass which is prepared by the same methods as describedabove.

Then, 97 wt.-% ofbiphenyl-4-yl(9,9-diphenyl-9H-fluoren-2-yl)-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-amine(CAS 1242056-42-3) and 3 wt.-% of2,2′,2″-(cyclopropane-1,2,3-triylidene)tris(2-(p-cyanotetraflubrophenyl)acetonitrile)is vacuum deposited on the ITO elec-trode, to form a HIL having athickness of 10 nm. Thenbiphenyl-4-yl(9,9-diphenyl-9H-fluoren-2-yl)-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-amine(CAS 1242056-42-3) is vacuum deposited on the HIL, to form a HTL havinga thickness of 125 nm. ThenN,N-bis(4-(dibenzo[b,d]furan-4-yl)phenyl)-[1,1′:4′,1″-terphenyl]-4-amine is deposed directly on top of the HTL to forman EBL with a thickness of 5 nm.

97 wt.-% of 2-(10-phenyl-9-anthracenyl)-benzo[b]naphtho[2,3-d]furan as ahost and 3 wt.-% of NUBD370 (Sun Fine Chemicals) as a dopant aredeposited on the EBL, to form a blue-emitting EML with a thickness of 20nm.

Then the first and second electron transport layer and optional electroninjection layer are deposed on the EML as described for bottom emissiondevices above.

The cathode electrode layer is evaporated at ultra-high vacuum of 10-7bar. Therefore, a thermal single co-evaporation of one or several metalsis performed with a rate of 0, 1 to 10 nm/s (0.01 to 1 Å/s) in order togenerate a homogeneous cathode electrode with a thickness of 5 to 1000nm.

60 nmbiphenyl-4-yl(9,9-diphenyl-9H-fluoren-2-yl)-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-amine (CAS 1242056-42-3) is deposed directly on top of thesecond cathode electrode layer.

The OLED stack is protected from ambient conditions by encapsulation ofthe device with a glass slide. Thereby, a cavity is formed, whichincludes a getter material for further protection.

To assess the performance of the inventive examples compared to theprior art, the current efficiency is measured under ambient conditions(20° C.). Current voltage measurements are performed using a Keithley2400 sourcemeter, and recorded in V. At 10 mA/cm² for bottom emissionand 10 mA/cm² for top emission devices, a calibrated spectrometer CAS140from Instrument Systems is used for measurement of CIE coordinates andbrightness in Candela. Lifetime LT of bottom emission device is measuredat ambient conditions (20° C.) and 10 mA/cm², using a Keithley 2400sourcemeter, and recorded in hours. Lifetime LT of top emission deviceis measured at ambient conditions (20° C.) and 8 mA/cm². The brightnessof the device is measured using a calibrated photo diode. The lifetimeLT is defined as the time till the brightness of the device is reducedto 97% of its initial value.

In bottom emission devices, the emission is predominately Lambertian andquantified in percent external quantum efficiency (EQE). To determinethe efficiency EQE in % the light output of the device is measured usinga calibrated photodiode at 10 mA/cm².

In top emission devices, the emission is forward directed,non-Lambertian and also highly dependent on the micro-cavity. Therefore,the efficiency EQE will be higher compared to bottom emission devices.To determine the efficiency EQE in % the light output of the de-vice ismeasured using a calibrated photodiode at 10 mA/cm².

Technical Effect of the Invention

The beneficial effect of the invention on the performance of bottomemission devices can be seen in Table 7, 8 and 9.

In Table 7, results are shown for fluorescent blue devices with a firstelectron transport layer comprising of a first organic aromatic matrixcompound, a second electron transport layer comprising of a polarorganic aromatic phosphine compound, and an electron injection layercomprising of lithium organic complex LiQ (comparative example 1 to 10and example 1 to 4) or Yb (comparative example 11 to 13 and example 4).

In comparative example 1, the first and second electron transport layercomprise of polar organic aromatic phosphine oxide A26. The dipolemoment of A26 is 2.68 eV, the reduction potential is −2.2 V and the LUMOis −2.64 eV. The operating voltage is 4.9 V and the external quantumefficiency EQE is 5.5%. The lifetime has not been measured as theefficiency is quite low. In comparative example 2, the first and secondelectron transport layers comprise a different polar phosphine oxidecompound. A18 is used instead of A26. The dipole moment of A18 is 4.64eV, the reduction potential is −2.62 V and the LUMO is −2.22 eV. Theperformance is even worse, as the operating voltage is slightly higherand the efficiency is reduced.

In comparative example 3, the first electron transport layer comprisespolar organic aromatic phosphine compound A26 and the second electrontransport layer comprises a mixture of polar organic aromatic phosphinecompounds A26 and A18. No improvement in operating voltage or efficiencyis observed.

In comparative example 4, the first electron transport layer comprisespolar phenanthroline compound PHEN-1, see structure below. PHEN-1 has adipole moment of approx. 3.6 Debye, a reduction potential of −2.29 V anda LUMO of −2.55 eV.

The second electron transport layer comprises a mixture of polarphenanthroline compound PHEN-1 and polar organic aromatic phosphinecompound A18. A small improvement in efficiency and reduction inoperating voltage are observed.

In comparative example 5, the first and second electron transport layercomprise first organic aromatic matrix compound ETM1-1. The dipolemoment of ETM1-1 is close to 0 Debye, the reduction potential is −2.45 Vand the LUMO is −2.55 eV. The efficiency is low 4.6% and the operatingvoltage is high at 7.4 V.

In comparative example 6, the first electron transport layer comprisesnon-polar ETM1-1 and the second electron transport layer comprises polarphosphine compound A18. No improvement in efficiency or operatingvoltage is observed.

In example 1, the first electron transport layer comprises non-polarETM1-1 and the second electron transport layer comprises a mixture ofnon-polar ETM1-1 and polar phosphine compound A18. The efficiency isimproved substantially to 7.1% EQE and the operating voltage is very lowat 4.3 V. The lifetime is dramatically improved to 119 hours, comparedto 15 and 32 hours for comparative examples 3 and 4. In summary, asubstantial benefit is observed for an electron transport layer stackaccording to the present invention.

In example 2, the first electron transport layer comprises non-polartriazine compound ETM1-32 and the second electron transport layercomprises polar phosphine compound A18. Triazine compound ETM1-32 has adipole moment of 1.03 Debye, a reduction potential of −2.22 V and a LUMOof −2.62 V. Again the efficiency is very high at 7.2% EQE and theoperating voltage is comparatively low at 4.5 V. The lifetime is good at83 hours. All performance parameters are improved over comparativeexample 7 to 9 which do not contain a mixture of non-polar and polarmatrix compound in the second electron transport layer.

In example 3, the first electron transport layer comprises non-polardibenzo[c,h]acridine compound ETM1-15 and polar phosphine compound A18.Dibenzo[c,h]acridine compound ETM1-15 has a dipole moment of 1.8 Debye,a reduction potential of −2.26 V and a LUMO of −2.58 eV. Efficiency andoperating voltage are improved over comparative example 10, which doesnot contain a mixture of matrix compounds in the second electrontransport layer.

In example 4, the first electron transport layer comprises non-polartriazine compound ETM1-32 and the second electron transport layercomprises polar phosphine compound A18. The electron injection layercomprises 2 nm Yb. Again the efficiency is very high at 6.9% EQE and theoperating voltage is comparatively low at 4.7 V. The lifetime is good at59 hours. All performance parameters are improved over comparativeexample 11 to 13 which do not contain a mixture of non-polar and polarmatrix compound in the second electron transport layer.

In Table 8, results are shown for fluorescent blue bottom emissiondevices with a first electron transport layer comprising a first organicaromatic matrix compound and a second electron transport layercomprising a first and second matrix compound and a non-emitter dopantselected from lithium organic complex Li-1. Comparative examples 14 to18 and examples 5 and 6 do not contain an electron injection layer.Comparative examples 19 and 20 and example 7 contain an electroninjection layer formed from 1.5 nm LiQ. Comparative examples 21 and 22and example 8 contain an electron injection layer formed from 2 nm Yb.

In comparative example 14, the first electron transport layer comprisespolar phenanthroline compound PHEN-1 and the second electron transportlayer comprises a mixture of PHEN-1, polar phosphine compound A18 andlithium organic complex Li-1. The efficiency is 6.4% EQE and theoperating voltage is 5 V. The lifetime is very short at 15 hours.

In comparative example 15, the first electron transport layer comprisingnon-polar dibenzo[c,h]acridine compound ETM1-15 and the second electrontransport layer comprises ETM1-15 and Li-1. The efficiency is reduced to5.7% EQE and the operating voltage is increased to 6.6 V.

In comparative example 16, the first electron transport layer comprisingnon-polar dibenzo[c,h]acridine compound ETM1-15 and the second electrontransport layer comprises polar phosphine compound A18 and Li-1. Theefficiency is increased to 6.3% EQE and the operating voltage is reducedto 3.7 V.

In example 5, the first electron transport layer comprising non-polardibenzo[c,h]acridine compound ETM1-15 and the second electron transportlayer comprises a mixture of ETM1-15, polar phosphine compound A18 andLi-1. The efficiency is increased to 7% EQE and the operating voltage isstill low at 4 V. The lifetime is 30 hours. All performance parametersare improved over comparative examples 14 to 16.

In example 6, the first electron transport layer comprising non-polartriazine compound ETM1-32 and the second electron transport layercomprises a mixture of ETM1-32, polar phosphine compound A18 and Li-1.The efficiency is substantially increased to 9.9% EQE and the operatingvoltage is still low at 4.6 V. The lifetime is 21 hours. Efficiency andlifetime are improved over comparative examples 14 to 18.

In comparative example 19, the first and second electron transport layercomprise the same maxtrix non-polar triazine matrix compound ETM1-32.The second electron transport layer additionally comprises Li-1. LiQ isused as electron injection layer. The efficiency is still high at 7.3%EQE but the operating voltage is also high at 6.2 V.

In comparative example 20, the first electron transport layer comprisesnon-polar triazine compound ETM1-32 and the second electron transportlay& comprises polar phosphine compound A18 and Li-1. The efficiency isstill high at 7.6% EQE and the operating voltage is reduced compared toexample 5, but this comes at the expense of having to deposit anadditional layer compared to example 5.

In example 7, the same ETL-stack is used as in example 6 butadditionally the devices contain an electron injection layer comprisingLiQ. The efficiency remains very high at 10% EQE, while the operatingvoltage is reduced to 4.4 V, thereby demonstrating the beneficial effectof an EIL on the operating voltage.

In example 8, the same ETL-stack is used as in example 6 and 7 butadditionally the devices contain an electron injection layer comprisingYb. The efficiency is still high at 9.7% EQE and the voltage is furtherimproved to 4.3 V. The lifetime is unaffected. In particular, theefficiency is improved compared to comparative examples 14 to 22.

In summary, very high efficiency and good lifetime can be obtained withthe ETL-stack according to the present invention. If a further reductionin operating voltage is desired, this can be achieved with an electroninjection layer. However, even without electron injection layer theoperating voltage is within the range suitable for mass production ofdevices.

In Table 9, results are shown for fluorescent blue bottom emissiondevices comprising a first electron transport layer comprising a firstorganic aromatic matrix compound and a second electron transport layercomprising a mixture of first organic aromatic matrix compound, polarorganic aromatic phosphine compound and a non-emitter dopant selectedfrom zero-valent ytterbium metal.

Comparative examples 23 to 25 and example 9 do not contain an electroninjection layer. Comparative example 26 and 27 and example 10 contain anelectron injection layer formed from 1.5 nm LiQ. Comparative examples 28and 29 and example 11 contain an electron injection layer formed from 2nm Yb.

In comparative example 23, the first electron transport layer comprisespolar phenanthroline compound PHEN-2 and the second electron transportlayer comprises a mixture of PHEN-2, polar phosphine compound A18 and2.5 wt.-% Yb. The dipole moment of PHEN-2 is 2.53 Debye, the reductionpotential is −2.45 V and the LUMO is −2.39 eV. The efficiency is 5.7%EQE and the operating voltage is 3.3 V.

In comparative example 24, the first and second electron transportlayers comprise non-polar dibenzo[c,h]acridine compound ETM1-15. Thesecond electron transport layer additionally comprises 5 wt.-% Yb. Theefficiency is reduced compared to comparative example 23 and theoperating voltage is dramatically increased.

In comparative example 25, the first electron transport layer comprisesnon-polar dibenzo[c,h]acridine compound ETM1-15 and the second electrontransport layer comprises polar phosphine compound A18 and 5 wt.-% Yb.The efficiency is increased to 6.5% EQE and the operating voltage isvery low at 3.4 V.

In example 9, the first electron transport layer comprises non-polardibenzo[c,h]acridine compound ETM1-15 and the second electron transportlayer comprises a mixture of ETM1-15, polar phosphine compound Alb and2.5 wt.-% Yb. The efficiency is substantially increased to 8.5 EQE andthe operating voltage is still very low at 3.6 V. The lifetime is 32hours. In particular, the efficiency is improved over comparativeexamples 23 to 25.

In example 10, the ETL-stack is the same as in example 9 but the devicescontain additionally an electron injection layer formed from 1.5 nm LiQ.Efficiency and operating voltage are unchanged compared to example 9.Performance is improved over comparative examples 26 and 27 which do notcontain the mixture of matrix compounds in the second electron transportlayer.

In example 11, the same ETL-stack is used as in example 9 and 10.Efficiency, operating voltage and lifetime are unchanged compared toexample 9 and 10. In summary, when the second electron transport layercomprises a non-emitter dopant selected from zero-valent metal, highperformance can be achieved even without an electron injection layer.

A substantial time saving is achieved if no electron injection layer hasto be deposited.

Another aspect is directed to an organic light-emitting diode (OLED)comprising more than one emission layer (EML) 150, for example two,three or four emission layers may be present. An organic light-emittingdiode (OLED) comprising more than one emission layer is also describedas a tandem OLED or stacked OLED.

Another aspect is directed to a device comprising at least one organiclight-emitting diode (OLED). A device comprising organic light-emittingdiodes (OLED) is for example a display or a lighting panel.

TABLE 7 Bottom emission device comprising an emission layer and anETL-stack comprising a first and second electron transport layer and anelectron injection layer d (ETL1)/ wt.-% wt.-% d (ETL2)/ d (EIL)/ U at10 EQE*²/ ETL1 nm ETL2 ETM1 ETM2 nm EIL nm mA/cm²/V % LT/h ComparativeA26 6 A26 100 0 31 LiQ 1.5 4.9 5.5 na example 1 Comparative A18 6 A18100 0 31 LiQ 1.5 5.1 5.3 na example 2 Comparative A26 6 A26:A18 80 20 31LiQ 1.5 5.1 5.6 15 example3 Comparative PHEN-1 4 PHEN-1:A18 80 20 31 LiQ1.5 4 6.4 32 example 4 Comparative ETM1-1 6 ETM1-1 100 0 31 LiQ 1.5 7.44.6 na example 5 Comparative ETM1-1 6 A18 0 100 31 LiQ 1.5 5.6 5.2 naexample 6 Example 1 ETM1-1 6 ETM1-1:A18 80 20 31 LiQ 1.5 4.3 7.1 119 Comparative A18 6 A18 100 0 31 LiQ 1.5 5.5 4.3 na example 7 ComparativeETM1-32 6 ETM1-32 100 0 31 LiQ 1.5 6.8 6.6 na example 8 ComparativeETM1-32 6 A18 0 100 31 LiQ 1.5 5.9 5.3 na example 9 Example 2 ETM1-32 6ETM1-32:A18 80 20 31 LiQ 1.5 4.5 7.2 83 Comparative ETM1-15 6 A18 0 10031 LiQ 1.5 5.5 4.3 na example 10 Example 3 ETM1-15 6 ETM1-15:A18 80 2031 LiQ 1.5 4.3 6.6 45 Comparative A18 6 A18 100 0 31 Yb 2 5.1 4.9 naexample 11 Comparative ETM1-32 6 ETM1-32 100 0 31 Yb 2 7.9 6 na example12 Comparative ETM1-32 6 A18 0 100 31 Yb 2 5.9 5.2 na example 13 Example4 ETM1-32 6 ETM1-32:A18 80 20 31 Yb 2 4.7 6.9 59

TABLE 8 Bottom emission device comprising an emission layer and anETL-stack comprising a first and second electron transport layer and anoptional electron injection layer. The second electron transport layercomprises alkali organic complex Li-1 wt.-% Li d (ETL1)/ wt.-% wt.-%organic d (ETL2)/ d (EIL)/ U at 10 EQE*²/ ETL1 nm ETL2 ETM1 ETM2 complexnm EIL nm mA/cm²/V % LT/h Comparative PHEN-1 4 PHEN-1:A18:Li-1 50 35 1531 na 0 5 6.4 15 example 14 Comparative ETM1-15 6 ETM1-15:Li-1 70 0 3031 na 0 6.6 5.7 na example 15 Comparative ETM1-15 6 A18:Li-1 0 70 30 31na 0 3.7 6.3 na example 16 Example 5 ETM1-15 6 ETM1-15:A18:Li-1 50 20 3031 na 0 4 7 30 Comparative ETM1-32 5 ETM1-32:Li-1 70 0 30 31 na 0 8 5.9na example 17 Comparative ETM1-32 5 A18:Li-1 0 70 30 31 na 0 3.8 7.5 naexample 18 Example 6 ETM1-32 5 ETM1-32:A18:Li-1 50 20 30 31 na 0 4.6 9.921 Comparative ETM1-32 5 ETM1-32:Li-1 70 0 30 31 LiQ 1.5 6.2 7.3 naexample 19 Comparative ETM1-32 5 A18:Li-1 0 70 30 31 LiQ 1.5 3.75 7.6 naexample20 Example 7 ETM1-32 5 ETM1-32:A18:Li-1 50 20 30 31 LiQ 1.5 4.410 na Comparative ETM1-32 5 ETM1-32:Li-1 70 0 30 31 Yb 2 5.85 7.4 naexample 21 Comparative ETM1-32 5 A18:Li-1 0 70 30 31 Yb 2 3.7 7.4 naexample 22 Example 8 ETM1-32 5 ETM1-32:A18:Li-1 50 20 30 31 Yb 2 4.3 9.722

TABLE 9 Bottom emission device comprising an emission layer and anETL-stack comprising a first and second electron transport layer and anoptional electron injection layer. The second electron transport layercomprises a zero-valent metal d (ETL1)/ wt.-% wt.-% wt.-% d (ETL2)/ d(EIL)/ U at 10 EQE*²/ ETL1 nm ETL2 ETM1 ETM2 metal nm EIL nm mA/cm²/V %LT/h Comparative PHEN-2 5 PHEN-2:A18:Yb 50 47.5 2.5 29 na 0 3.3 5.7 naexample 23 Comparative ETM1-15 5 ETM1-15:Yb 95 0 5 31 na 0 7.1 4 naexample 24 Comparative ETM1-15 5 A18:Yb 0 95 5 31 na 0 3.4 6.5 naexample 25 Example 9 ETM1-15 5 ETM1-15:A18:Yb 50 47.5 2.5 31 na 0 3.68.5 32 Comparative ETM1-15 5 ETM1-15:Yb 95 0 5 31 LiQ 1.5 6.7 4.2 naexample 26 Comparative ETM1-15 5 A18:Yb 0 95 5 31 LiQ 1.5 3.4 6.5 naexample 27 Example 10 ETM1-15 5 ETM1-15:A18:Yb 50 47.5 2.5 31 LiQ 1.53.6 8.5 na Comparative ETM1-15 5 ETM1-15:Yb 95 0 5 31 Yb 2 6.7 4.1 naexample 28 Comparative ETM1-15 5 A18:Yb 0 95 5 31 Yb 2 3.4 6.5 naexample 29 Example 11 ETM1-15 5 ETM1-15:A18:Yb 50 47.5 2.5 31 Yb 2 3.68.4 31

The invention claimed is:
 1. Organic light emitting diode comprising: atleast one anode electrode; at least one emission layer, wherein theemission layer comprises at least one emitter dopant that emits visiblelight at operation of the OLED; an electron transport layer stack of atleast two electron transport layers, and wherein a) the first electrontransport layer comprises i) a first organic aromatic matrix compoundhaving a MW of about ≥400 to about ≤1000 and a dipole moment of about ≥0Debye and about ≤2.5 Debye, wherein the first electron transport layeris free of a polar organic aromatic phosphine compound; and b) thesecond electron transport layer comprises two organic aromatic matrixcompounds, which are a mixture of: i) the first organic aromatic matrixcompound; and ii) a polar organic aromatic phosphine compound having aMW of about ≥400 to about ≤1000, and a dipole moment of about >2.5 Debyeand about ≤10 Debye; and at least one cathode electrode layer; whereinthe electron transport layer stack is arranged between the emissionlayer and the cathode electrode layer, the first electron transportlayer is in direct contact with the second electron transport layer, andwherein the first electron transport layer is arranged nearer to theemission layer and the second electron transport layer is arrangednearer to the cathode electrode layer; wherein the organic lightemitting diode further comprises an electron injection layer, whereinthe electron injection layer comprises a metal compound; and wherein theelectron injection layer is sandwiched between the electron transportlayer stack and the cathode electrode layer.
 2. The organic lightemitting diode according to claim 1, wherein the electron transportlayer stack is free of an emitter dopant which emits visible light atoperation of the OLED.
 3. The organic light emitting diode according toclaim 1, wherein the first electron transport layer is free of anon-emitter dopant and the second electron transport layer comprises anon-emitter dopant, wherein the non-emitter dopant is a metal compound.4. The organic light emitting diode according to claim 3, wherein thezero-valent metal is selected from the group consisting essentially ofalkali metal, alkaline earth metal, rare earth metal ager a group 3transition metal, and a combination thereof.
 5. The organic lightemitting diode according to claim 1, wherein the polar organic aromaticphosphine compound of the second electron transport layer has theFormula Ia:

wherein: X is selected from O, S, or Se; R¹ and R² are independentlyselected from C₁ to C₁₂ alkyl, substituted or unsubstituted C₆ to C₂₀aryl or substituted or unsubstituted C₅ to C₂₀ heteroaryl; or R¹ and R²are bridged with an alkene-di-yl group forming with the P atom asubstituted or unsubstituted five, six or seven membered ring; and A¹ isphenyl or selected from Formula (II):

wherein R³ is selected from C₁ to C₈ alkane-di-yl, substituted orunsubstituted C₆ to C₂₀ arylene, or substituted or unsubstituted C₅ toC₂₀ heteroarylene; or A¹ is selected from Formula (III)

wherein n is selected from 0 or 1; m is selected from 1 or 2; o isselected from 1 or 2; and m is 1 if o is 2; Ar¹ is selected fromsubstituted or unsubstituted C₆ to C₂₀ arylene and substituted orunsubstituted C₅ to C₂₀ heteroarylene; Ar² is selected from substitutedor unsubstituted C₁₈ to C₄₀ arylene and substituted or unsubstituted C₁₀to C₄₀ heteroarylene; R⁴ is selected from H, C₁ to C₁₂ alkyl,substituted or unsubstituted C₆ to C₂₀ aryl and substituted orunsubstituted C₅ to C₂₀ heteroaryl.
 6. The organic light emitting diodeaccording to claim 5, wherein Ar¹ is selected from substituted C₆ to C₂₀arylene, and/or substituted C₅ to C₂₀ heteroarylene, wherein the C₆ toC₂₀ arylene, and/or C₅ to C₂₀ heteroarylene is substituted with at leastone C₁ to C₁₂ alkyl and/or at least one C₁ to C₁₂ heteroalkyl group; andAr² is selected from substituted C₁₈ to C₄₀ arylene and/or substitutedC₁₀ to C₄₀ heteroarylene, wherein the C₁₈ to C₄₀ arylene and/or C₁₀ toC₄₀ heteroarylene is substituted with at least one C₁ to C₁₂ alkyland/or at least one C₁ to C₁₂ heteroalkyl group.
 7. The organic lightemitting diode according to claim 5, wherein R¹ and R² are independentlyselected from substituted C₆ to C₂₀ aryl, or substituted C₅ to C₂₀heteroaryl, wherein the C₆ to C₂₀ aryl, and/or C₅ to C₂₀ heteroaryl issubstituted with at least one C₁ to C₁₂ alkyl and/or at least one C₁ toC₁₂ heteroalkyl group; and/or R³ is independently selected fromsubstituted C₆ to C₂₀ arylene, or substituted C₅ to C₂₀ heteroarylene,wherein the C₆ to C₂₀ arylene, and/or C₅ to C₂₀ heteroarylene issubstituted with at least one C₁ to C₁₂ alkyl and/or at least one C₁ toC₁₂ heteroalkyl group; and/or R⁴ is independently selected fromsubstituted C₆ to C₂₀ aryl, or substituted C₅ to C₂₀ heteroaryl, whereinthe C₆ to C₂₀ aryl, and/or C₅ to C₂₀ heteroaryl is substituted with atleast one C₁ to C₁₂ alkyl and/or at least one C₁ to C₁₂ heteroalkylgroup.
 8. The organic light emitting diode according to claim 5, whereinfor o=2, the polar organic aromatic phosphine compound is a compoundhaving the Formula Ib:

o=1, the polar organic aromatic phosphine compound is a compound havingthe Formula Ic, Id, le or If:


9. The organic light emitting diode according to claim 5, wherein R¹ andR² is independently selected from C₁ to C₄ alkyl, unsubstituted orsubstituted C₆ to C₁₀ aryl, or unsubstituted or substituted C₅ to C₁₀heteroaryl, wherein the C₆ to C₁₀ aryl, and/or C₅ to C₁₀ heteroaryl issubstituted with at least one C₁ to C₁₂ alkyl and/or at least one C₁ toC₁₂ heteroalkyl group; and/or X is O or S; and/or R³ is selected from C₁to C₆ alkane-di-yl, unsubstituted or substituted C₆ to C₁₀ arylene orunsubstituted or substituted C₅ to C₁₀ heteroarylene; and/or R⁴ isselected from H, phenyl, biphenyl, terphenyl, fluorenyl, naphthyl,anthranyl, phenanthryl, pyrenyl, carbazoyl, dibenzofuranyl,dinapthofuranyl; and/or n is 0, 1 or 2; m is 1 or 2 and n is 0 or 1, orm is 2 and n is 2; and/or Ar¹ is selected from the group consisting ofphenylene, biphenylene, terphenylene, naphthylene, fluorenylene,pyridylene, quinolinylene, and pyrimidinylene; and/or Ar² is selectedfrom the group consisting of fluorenylene, anthranylene, pyrenylene,phenanthrylene, carbazoylene, benzo[c]acridinylene,dibenzo[c,h]acridinylene, and dibenzo[a,j]acridinylene.
 10. The organiclight emitting diode according to claim 5, wherein R¹, R², R³, R⁴, Ar¹and/or Ar² are unsubstituted.
 11. The organic light emitting diodeaccording to claim 5, wherein Ar² is selected from a substituentaccording to Formula IVa to IVh:


12. The organic light emitting diode according to claim 5, wherein thepolar organic aromatic phosphine compound is selected from a compoundaccording to Formula A1 to A27:


13. A method of manufacturing an organic light emitting diode, accordingto claim 1, wherein on a substrate an anode electrode is deposited andon the anode electrode the other layers of hole injection layer, holetransport layer, optional an electron blocking layer, emission layer,optional hole blocking layer, an electron transport layer stackcomprising at least a first electron transport layer and a secondelectron transport layer, optional an electron injection layer, and acathode electrode layer, are deposited in that order; or the layers aredeposited the other way around, starting with the first cathodeelectrode layer.
 14. Electronic device comprising at least one organiclight emitting diode, according to claim
 1. 15. The organic lightemitting diode according to claim 3, wherein the metal compound isselected from the group consisting of a metal halide, a metal organiccomplex, a zero-valent metal, and a combination thereof.
 16. The organiclight emitting diode according to claim 15, wherein the metal organiccomplex has the formula VII:

wherein M is an alkali metal ion, and each of A¹-A⁴ is independentlyselected from substituted or unsubstituted C₆-C₂₀ aryl or substituted orunsubstituted C₂-C₂₀ heteroaryl.
 17. The organic light emitting diode ofclaim 4, wherein the electron injection layer is arranged in directcontact with the cathode electrode layer.
 18. The organic light emittingdiode according to claim 4, wherein the zero-valent metal is selectedfrom the group consisting of Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, Yb, Sm,Eu, Nd, Tb, Gd, Ce, La, Sc, and Y.
 19. The organic light emitting diodeaccording to claim 4, wherein the zero-valent metal is selected from thegroup consisting of Li, Mg, Ba, and Yb.